Electronic device

ABSTRACT

A sturdy electronic device is provided. A reliable electronic device is provided. A novel electronic device is provided. An electronic device includes a first board, a second board, a display portion having flexibility, and a power storage device having flexibility. The first board and the second board face each other. The display portion and the power storage device are provided between the first board and the second board. The display portion includes a first surface facing the power storage device. The first surface includes a first region not fixed to the power storage device. The first region overlaps with a display region of the display portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electronic device, a display device,a light-emitting device, a power storage device, a driving methodthereof, or a manufacturing method thereof.

Note that electronic devices in this specification mean all deviceswhich operate by being supplied with electric power, and electronicdevices including power sources, electronic devices and electro-opticaldevices including power sources such as storage batteries, informationterminal devices including storage batteries, and the like are allelectronic devices. Electronic devices also mean all devices whichprocess information. Note that one embodiment of the present inventionis not limited to the above technical field. The technical field of oneembodiment of the invention disclosed in this specification and the likerelates to an object, a method, or a manufacturing method. In addition,one embodiment of the present invention relates to a process, a machine,manufacture, or a composition of matter. Specifically, examples of thetechnical field of one embodiment of the present invention disclosed inthis specification include a semiconductor device, a display device, aliquid crystal display device, a light-emitting device, a lightingdevice, a power storage device, a memory device, an imaging device, amethod for driving any of them, or a method for manufacturing any ofthem.

2. Description of the Related Art

Display devices used while being worn on human bodies, such as displaydevices mounted on heads, have recently been developed and are referredto as head-mounted displays or wearable displays. It is desired thatelectronic devices used while being worn on human bodies, such ashearing aids, have a light weight and a small size.

Along with a decrease in weight of electronic devices, it is demandedthat storage batteries included in electronic devices also have a lightweight and a small size.

Electronic book terminals including flexible display devices aredisclosed in Patent Documents 1 and 2.

REFERENCES [Patent Document 1] Japanese Published Patent Application No.2010-282181 [Patent Document 2] Japanese Published Patent ApplicationNo. 2010-282183 SUMMARY OF THE INVENTION

In order that a user can comfortably wear a display device used whilebeing worn on a human body, the display device needs to have a lightweight and a small size, and in addition, the whole electronic deviceincluding a driver device for the display device and a power sourceneeds to have a light weight.

Furthermore, a display device used while being worn on a human body andan electronic device including the display device need to be easilycarried around and to be sturdy.

When the display device and an electronic device including the displaydevice are worn on a human body and removed therefrom repeatedly,external stress such as bending is repeatedly applied to them.Consequently, a display portion, an external portion, a power storagedevice included in the display device or the electronic device, or thelike is broken in some cases.

An object of one embodiment of the present invention is to provide asturdy electronic device. Another object of one embodiment of thepresent invention is to provide a reliable electronic device. Anotherobject of one embodiment of the present invention is to provide a novelelectronic device.

Another object of one embodiment of the present invention is to providea sturdy display device. Another object of one embodiment of the presentinvention is to provide a reliable display device. Another object of oneembodiment of the present invention is to provide a novel displaydevice.

Another object of one embodiment of the present invention is to providean electronic device used while being worn on a human body. Anotherobject of one embodiment of the present invention is to provide anelectronic device used while being worn on an arm.

Another object of one embodiment of the present invention is to providea display device used while being worn on a human body. Another objectof one embodiment of the present invention is to provide a displaydevice used while being worn on an arm.

Another object of one embodiment of the present invention is to providea power storage device used while being worn on part of a human body.Another object of one embodiment of the present invention is to providea power storage device used while being worn on an arm.

Note that the descriptions of these objects do not disturb the existenceof other objects. In one embodiment of the present invention, there isno need to achieve all the objects. Other objects will be apparent fromand can be derived from the description of the specification, thedrawings, the claims, and the like.

One embodiment of the present invention is an electronic device whichincludes a first board, a second board, a display portion havingflexibility, and a power storage device having flexibility. The firstboard and the second board face each other. The display portion and thepower storage device are provided between the first board and the secondboard. The display portion includes a first surface facing the powerstorage device. The first surface includes a first region not fixed tothe power storage device. The first region overlaps with a displayregion of the display portion.

Another embodiment of the present invention is an electronic devicewhich includes a first board, a second board, a display portion havingflexibility, and a power storage device having flexibility. The firstboard and the second board face each other. The display portion and thepower storage device are provided between the first board and the secondboard. There is a space between the display portion and the powerstorage device.

Another embodiment of the present invention is an electronic devicewhich includes a first board, a second board, a display portion havingflexibility, a power storage device having flexibility, and an adhesivelayer. The display portion includes a circuit board having flexibility.The first board and the second board face each other. The displayportion and the power storage device are provided between the firstboard and the second board. The display portion is fixed to the firstboard with the adhesive layer provided therebetween. The power storagedevice is at least partly in contact with the second board. A region ofthe power storage device is apart from the first board.

Another embodiment of the present invention is an electronic devicewhich includes a first board, a second board, a display portion havingflexibility, and a power storage device having flexibility. The firstboard and the second board face each other. The display portion and thepower storage device are provided between the first board and the secondboard. A shock-absorbing buffer member is provided between the displayportion and the power storage device.

The electronic device of any of the above embodiments is preferably wornsuch that the second board is in contact with an arm of a user.

In any of the above embodiments, it is preferable that the displayportion include a first end portion and a second end portion; the powerstorage device include a third end portion and a fourth end portion; thefirst end portion and the third end portion be fixed to each other; andthe distance between the second end portion and the fourth end portionchange as the shape of the electronic device changes.

Another embodiment of the present invention is an electronic devicewhich includes a first housing having flexibility, a second housinghaving flexibility, a display portion having flexibility, and a powerstorage device having flexibility. The first housing includes a firstsurface having a light-transmitting property. The display portion isprovided inside the first housing. A region of the display portion is incontact with the first surface. The power storage device is providedinside the second housing. In the above embodiment, the electronicdevice is preferably worn such that the second housing is in contactwith an arm of a user.

According to one embodiment of the present invention, a sturdyelectronic device can be provided. According to one embodiment of thepresent invention, a reliable electronic device can be provided.According to one embodiment of the present invention, a novel electronicdevice can be provided.

According to one embodiment of the present invention, a sturdy displaydevice can be provided. According to one embodiment of the presentinvention, a reliable display device can be provided. According to oneembodiment of the present invention, a novel display device can beprovided.

According to one embodiment of the present invention, an electronicdevice used while being worn on part of a human body can be provided.According to one embodiment of the present invention, an electronicdevice used while being worn on an arm can be provided.

According to one embodiment of the present invention, a power storagedevice used while being worn on part of a human body can be provided.According to one embodiment of the present invention, a power storagedevice used while being worn on an arm can be provided.

According to one embodiment of the present invention, a display deviceused while being worn on a human body can be provided. According to oneembodiment of the present invention, a display device used while beingworn on an arm can be provided.

Note that the descriptions of these effects do not disturb the existenceof other effects. One embodiment of the present invention does notnecessarily achieve all the effects. Other effects will be apparent fromand can be derived from the description of the specification, thedrawings, the claims, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an electronic device of one embodimentof the present invention.

FIGS. 2A to 2D are cross-sectional views illustrating electronic devicesof one embodiment of the present invention.

FIGS. 3A and 3B are a perspective view and a cross-sectional view eachillustrating an electronic device of one embodiment of the presentinvention.

FIGS. 4A to 4C are cross-sectional views illustrating an electronicdevice of one embodiment of the present invention.

FIGS. 5A and 5B are cross-sectional views illustrating an electronicdevice of one embodiment of the present invention.

FIGS. 6A to 6C are cross-sectional views illustrating an electronicdevice of one embodiment of the present invention.

FIGS. 7A to 7C illustrate an electronic device according to oneembodiment of the present invention.

FIGS. 8A and 8B are cross-sectional views each illustrating anelectronic device of one embodiment of the present invention.

FIGS. 9A and 9B are cross-sectional views illustrating an electronicdevice of one embodiment of the present invention.

FIG. 10 is an external view of a thin storage battery.

FIGS. 11A and 11B are cross-sectional views of a thin storage battery.

FIG. 12 is a perspective view illustrating an electronic device of oneembodiment of the present invention.

FIGS. 13A and 13B illustrate a method for manufacturing a thin storagebattery.

FIGS. 14A and 14B illustrate a method for manufacturing a thin storagebattery.

FIG. 15 is an external view of a thin storage battery.

FIGS. 16A to 16C illustrate a radius of curvature of a surface.

FIGS. 17A to 17D illustrate a radius of curvature of a film.

FIGS. 18A and 18B illustrate a coin-type storage battery.

FIG. 19 is a cross-sectional view of a thin storage battery.

FIG. 20 is a top view of a display device.

FIG. 21 is a cross-sectional view of a display device.

FIG. 22 is a cross-sectional view of a display device.

FIG. 23 is a cross-sectional view of a display device.

FIG. 24 is a cross-sectional view of a display device.

FIG. 25 is a cross-sectional view of a display device.

FIG. 26 illustrates an electronic device of one embodiment of thepresent invention.

FIGS. 27A to 27D are schematic cross-sectional views illustrating adeposition principle.

FIG. 28 illustrates a structure of a deposition apparatus according toone embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described in detail belowwith reference to the drawings. However, the present invention is notlimited to the description below, and it is easily understood by thoseskilled in the art that modes and details disclosed herein can bemodified in various ways. Furthermore, the present invention is notconstrued as being limited to the description of the embodiments.

Note that a display device in this specification includes any of thefollowing modules in its category: a module in which a connector such asa flexible printed circuit (FPC) or a tape carrier package (TCP) isattached to a display panel (a display device); a module having a TCPprovided with a printed wiring board at the end thereof; and a modulehaving an integrated circuit (IC) directly mounted on a substrate overwhich a display element is formed, by a chip on glass (COG) method.

In this specification, the term “parallel” indicates that the angleformed between two straight lines is greater than or equal to −10° andless than or equal to 10°, and accordingly also includes the case wherethe angle is greater than or equal to −5° and less than or equal to 5°.In addition, the term “substantially parallel” indicates that the angleformed between two straight lines is greater than or equal to −30° andless than or equal to 30°. The term “perpendicular” indicates that theangle formed between two straight lines is greater than or equal to 80°and less than or equal to 100°, and accordingly also includes the casewhere the angle is greater than or equal to 85° and less than or equalto 95°. In addition, the term “substantially perpendicular” indicatesthat the angle formed between two straight lines is greater than orequal to 60° and less than or equal to 120°.

In this specification, trigonal and rhombohedral crystal systems areincluded in a hexagonal crystal system.

An electronic device of one embodiment of the present inventionpreferably includes a semiconductor device, a display device, a liquidcrystal display device, a light-emitting device, a lighting device, apower storage device, a memory device, an imaging device, or the like.

Embodiment 1

In this embodiment, an example of an electronic device 100 that can beworn on part of a human body will be described.

<Example of Electronic Device 100>

FIG. 1 is an example of a perspective view of the electronic device 100.

The electronic device 100 illustrated in FIG. 1 includes a displayportion 102, a board 112, and a power storage device 103 which is atleast partly in contact with the board 112. The power storage device 103is preferably positioned along a region of the board 112 where theradius of curvature is large. In the electronic device 100 illustratedin FIG. 1, the power storage device 103 and the display portion 102 arepositioned so as to at least partly overlap with each other. With such astructure, the inside of the electronic device can have high layoutflexibility.

The display portion 102 preferably includes a circuit board 104. Theelectronic device 100 may further include a circuit board 107. Thecircuit board 107 is preferably electrically connected to the powerstorage device 103 and the circuit board 104. The circuit board 107 mayinclude, for example, a driver circuit for driving the display portion102. The circuit board 107 is preferably provided with a convertercircuit for feeding power from the power storage device. In some cases,the display portion 102 and the circuit board 107 are collectivelyreferred to as a display module.

The electronic device 100 preferably includes a board 111. In the casewhere the electronic device 100 includes the board 111, the board 111and the board 112 are preferably fixed to each other with fasteners 131.The fasteners 131 may have a band-like shape as illustrated in FIG. 1 ormay have a screw-like shape. For example, the board 111 and the board112 may be provided with screw holes and fixed to each other with thefasteners 131 having a screw-like shape.

The board 111 and the board 112 may be fixed to each other by swaging.For example, the electronic device 100 may be fixed by inserting thefasteners 131 into the holes provided in the board 111 and the board 112and deforming (swaging) the fasteners 131. As the fasteners 131, forexample, rivets or the like can be used.

For the fasteners 131, a material such as a metal, a ceramic, or a resincan be used. As the metal, a material that is hard to rust whenpassivated is preferably used, and for example, stainless steel,magnesium, aluminum, or titanium can be used.

FIG. 2A is a cross-sectional view of the electronic device 100illustrated in FIG. 1. FIG. 2B illustrates a cross section which istaken along the dashed line A-B in FIG. 2A and which is substantiallyperpendicular to the cross section in FIG. 2A. Note that the scale ofFIG. 2B is larger than that of FIG. 2A for easy understanding.

The display portion 102 preferably includes a display element 152 and acircuit portion 153 over a board 151. The circuit portion 153 preferablyincludes a driver circuit for driving the display element 152. Thecircuit board 104 is preferably connected to the circuit portion 153 orthe like. The circuit board 104 may include a driver circuit for drivingthe display element 152.

A display region of the display portion 102 may refer to, for example, aregion where the display element 152 is provided, or may refer to asurface on which an image, text information, or the like is displayed inthe electronic device 100. For example, the shape of the display regioncan be changed by providing, for example, a light-blocking plate on afront or rear side of the board 111 to block part of light from theregion where the display element 152 is provided. Although the regionwhere the display element 152 is provided has a substantiallyquadrangular shape in the example illustrated in FIG. 1, the regionwhere the display element is provided is not limited to the quadrangularshape or the like.

The board 151 preferably has flexibility. When the board 151 hasflexibility, the display portion 102 can have flexibility, for example.

Examples of the board 151 include a plastic substrate. A substratehaving flexibility may be attached to a board or the like. A displaydevice having flexibility can be manufactured with the use of the board151 having flexibility. When the display device has flexibility, thedisplay device can be attached to a curved surface or an irregularshape, whereby a variety of applications are achieved. For example, theboard 151 having flexibility such as a plastic substrate is used,whereby the display device can be thinner and more lightweight. Inaddition, the display device in which the board 151 having flexibilitysuch as a plastic substrate is used is hardly broken, and can withstandimpacts well when dropped, for example.

The electronic device 100 can be worn on a human body such as an arm.When the electronic device 100 is worn on, for example, part of a humanbody such as an arm, the board 112 is in contact with the part of thebody.

The board 112 preferably has a shape that fits around an arm. Theelectronic device 100 may be mounted on an arm of a robot or the like.Examples of the robot include a working robot, a robot attached to anapparatus, and a humanoid robot.

The board 112 preferably has a round shape. Alternatively, the board 112may include a curved surface and a flat surface. The board 112preferably has a shape along a curved surface, for example.Alternatively, the board 112 preferably has a shape along a side surfaceof an elliptical cylinder. The board 112 may partly have, for example,an arch-like shape, a C-like shape, an elliptical shape, or anelliptical shape part of which is cut. When the board 112 has such around shape, the electronic device 100 can fit a body such as an armmore snugly. The electronic device 100 can be put around an armaccording to the shape of the arm. Furthermore, the board 112 may have across section along three sides of a quadrangle.

The board 112 may have a shape along a cylindrical object, for example.Specifically, the board 112 may have a shape along a cylinder, anelliptical cylinder, or a prism. Alternatively, the board 112 may have ashape along a circular cone shape or a pyramid shape.

The board 112 is preferably configured to be mounted on a cylindricalobject. Here, examples of the cylindrical object include a column shape,a cone shape, a pyramid shape, or a cylinder whose orientation of a sidesurface continuously changes, and the like.

In wearing the electronic device 100 on a body such as an arm, the shapeof the electronic device 100 may be changed by an external force. Forexample, by changing the shape of the board 112 or the like indirections of arrows 105 in FIG. 2A, the electronic device 100 can beworn more easily. Therefore, the board 112 preferably has flexibility.

As the shape of the board 112 changes, the shape of another portion ofthe electronic device 100 may change. Therefore, in some cases, otherportions of the electronic device 100 also preferably have flexibility.For example, the display portion 102 preferably has flexibility. Theboard 111 and the power storage device 103 also preferably haveflexibility. Here, a film or the like may be used as the board 111.

When an external force is applied to the electronic device 100, theshape of the electronic device 100 changes. As the shape of theelectronic device 100 changes, the shape of the power storage device 103changes.

The amount of change in shape of the power storage device 103 owing tothe external force applied to the electronic device 100 is preferablymaintained while the external force is being applied. For example, theamount of change in shape of the power storage device 103 caused inwearing the electronic device 100 on an arm or the like is preferablymaintained while the electronic device 100 is being worn. Since theamount of change in shape of the power storage device 103 is maintained,the power storage device 103 is suitable for being mounted on theelectronic device 100 having a smaller radius of curvature. In addition,the power storage device 103 is suitable for use in the electronicdevice 100 which is movable. Furthermore, since the amount of change inshape of the power storage device 103 is maintained, the shape of theelectronic device 100 fits a body part well.

For example, in the case where the power storage device 103 has highelasticity or the like, the shape of the power storage device 103 maytemporarily change as the shape of the electronic device 100 changes,but may return to the original shape later. That is, the amount ofchange in shape of the power storage device 103 from the original shapemay decrease with time. When the power storage device 103 returns to theoriginal shape, another portion of the electronic device 100 may bedistorted, for example.

The electronic device 100 may include sealing portions 121 asillustrated in FIG. 2C. FIG. 2C illustrates an example in which theelectronic device 100 in FIG. 2B is provided with the sealing portions121. By providing the sealing portions 121, the hermeticity of a housingincluding the board 111, the board 112, and the sealing portions 121 canbe further improved in some cases. Furthermore, when the shapes of theboard 111 and the board 112 are changed by an external force, thesealing portions 121 relieve the shape change due to the external force;thus, the whole structure of the electronic device 100 can bemaintained.

For the sealing portions 121, for example, a resin can be used. As aresin, for example, an elastomer can be used.

FIG. 2D illustrates another example in which the electronic device 100includes the sealing portions 121. A cross section of the electronicdevice 100 illustrated in FIG. 2D differs from that in FIG. 2B in theshape of the board 111 and the presence of the sealing portions 121. Inthe cross section illustrated in FIG. 2D, the board 111 has end portionsthat are bent in an L-like shape. The electronic device 100 has ahousing including the board 111 whose end portions are bent in an L-likeshape, the sealing portions 121, and the board 112.

The sum of the thicknesses of the display element 152 and the board 151in the display portion 102 is preferably greater than or equal to 1 μmand less than or equal to 1 mm, further preferably, greater than orequal to 5 μm and less than or equal to 200 μm. The thickness of thepower storage device 103 is, for example, greater than or equal to 50 μmand less than or equal to 30 mm and may be larger than the thickness ofthe display element.

When an external force is applied to objects with different thicknesses,the objects may differ from each other in how they are bent by theexternal force, specifically, the degree of change in radius ofcurvature, or the like. The degree of change in radius of curvaturerefers to, for example, the amount of change in shape by an externalforce, the temporal change in the amount of change, the response speedof the change, or the like.

Therefore, when an external force is applied to a region where twoobjects with different thicknesses are fixed to each other, either ofthe objects may be distorted, which might result in a crack or abreakage. The region where the two objects are fixed to each otherrefers to, for example, a region where the contacting surfaces of theobjects are attached to each other, or the like.

A case where the shape of the electronic device 100 is changed by anexternal force in wearing the electronic device 100 on an arm or thelike will be considered here. In such a case, it is preferable thatthere be a region where the display portion 102 and the power storagedevice 103 are not fixed to each other.

Therefore, a space is preferably provided between the power storagedevice 103 and the display portion 102. Alternatively, a deformable orfluid substance is preferably provided between the power storage device103 and the display portion 102. For example, a liquid such as water ora gel substance may be provided. Alternatively, a region of the displayportion 102 is preferably not attached to the power storage device 103.It is particularly preferable that the region where the display elementis provided in the display portion 102 not be attached to the powerstorage device 103. Alternatively, a region of the display portion 102is preferably apart from the power storage device 103. Such structurescan improve the reliability of the display portion 102 and the powerstorage device 103. In addition, such structures can suppress thedistortion of the display portion 102 and the power storage device 103.Furthermore, such structures can suppress the generation of a crack or abreakage in the display portion 102 and the power storage device 103.

Surfaces of the power storage device 103 and the display portion 102 arepreferably in contact with each other and easily slide on each other.

It is preferable that the display portion 102 include a first surfacewhich faces the power storage device 103 and the first surface include afirst region which is not fixed to the power storage device 103. It isalso preferable that the first region overlap with the display element152 of the display portion 102.

It is preferable that there be a first region where the display portion102 and the power storage device 103 are not fixed to each other. Theremay be the first region where the display portion 102 and the powerstorage device 103 are not fixed to each other and one region or two ormore regions where they are fixed to each other. For example, thedisplay portion 102 and the power storage device 103 may be fixed toeach other in one end region. Alternatively, the display portion 102 andthe power storage device 103 may be fixed to each other in two or moreregions, i.e., in one end region and in another or other regions. Thedisplay portion 102 and the power storage device 103 can be fixed toeach other with, for example, an adhesive layer or the like.Alternatively, the display portion 102 and the power storage device 103may be fixed to each other with a buffer, a porous material, or the likeprovided therebetween.

Alternatively, it is preferable that the display portion 102 have an endportion 171 and an end portion 172, the power storage device 103 have anend portion 173 and an end portion 174, the end portion 171 and the endportion 173 be fixed to the circuit board 107, and the end portion 172and the end portion 174 not be fixed to each other, as illustrated inFIG. 2A.

Alternatively, it is preferable that the power storage device 103 andthe display portion 102 be in contact with each other and the contactingsurfaces thereof easily slide on each other.

When the contacting surfaces of the power storage device 103 and thedisplay portion 102 easily slide on each other, an external forceapplied to either the power storage device 103 or the display portion102 may be prevented from being easily applied to the other. A reductionin the effect of an external force on each other can prevent deformationsuch as distortion.

In some cases, an exterior body of the power storage device 103 and afilm provided with the display element in the display portion 102 areformed using different materials. In such cases, the power storagedevice 103 and the display portion 102 may differ from each other in howthey are bent by an external force, specifically, the degree of changein radius of curvature, or the like. In the case where the power storagedevice 103 and the display portion 102 differ from each other in howthey are bent by the external force, specifically, the degree of changein radius of curvature, or the like, either the exterior body of thepower storage device 103 or the display portion 102 or both might bedistorted. The display portion 102 is particularly likely to bedistorted because it is thin.

When the electronic device 100 is dropped or hit by an object or thelike, components of the electronic device 100 may receive an impact.

Even in such a case, when a space is provided between the power storagedevice 103 and the display portion 102, the space can absorb the impactand can thus weaken an impact from the outside. As one example, a casewhere the electronic device 100 and an object hit each other and theboard 111 and the object are brought into contact with each other isconsidered. In such a case, an impact received by the board 111 does notdirectly reach the power storage device 103 and the circuit board 107and can be weakened.

As the circuit board 104, for example, a circuit board havingflexibility can be used. As the circuit board having flexibility, aflexible printed circuit (FPC) in which a flexible resin film isprovided with a wiring is preferably used. In the case where an FPC isused as the circuit board 104, the circuit board 104 can change itsshape as the electronic device 100 changes its shape when it is beingworn, and the circuit board 104 or the like can be prevented from beingbroken owing to a crack in a connection portion between the circuitboard 104 and the circuit portion 153 or the like or in a connectionportion between the circuit board 104 and the circuit board 107.

In the electronic device 100, the display portion 102 may be at leastpartly in contact with the board 111. Alternatively, in the electronicdevice 100, an adhesive layer or a layer including a touch sensor may beprovided between the display portion 102 and the board 111. For example,as the adhesive layer, an adhesive sheet may be attached to the board111 and the display portion 102 may be attached to the adhesive sheet.Alternatively, the board 111 may include a touch sensor. In the casewhere the display portion 102 is at least partly in contact with aninner surface of the board 111, the shape of the display portion 102 caneasily fit the shape of the inner surface of the board 111 when thedisplay portion 102 has flexibility. Even in the case where the shape ofthe board 111 is changed by an external force, the display portion 102can be prevented from being degraded or broken.

Each of the boards 111 and 112 preferably has a curved surface.Furthermore, each of the cross sections of the boards 111 and 112preferably has a circular shape or a circular arc shape, for example.

When the electronic device 100 is being worn or removed, it is preferredthat regions with a large radius of curvature in the cross sections ofthe boards 111 and 112 not be substantially deformed and end portions inthe cross sections of the boards 111 and 112 be flexible. For example,the cross sections of the boards 111 and 112 preferably have a C-likeshape, an elliptical shape, or an elliptical shape part of which is cut.When the cross sections of the boards 111 and 112 have such a roundshape, the electronic device 100 can fit a body such as an arm moresnugly. For example, in the case where the electronic device 100 is wornon an arm, the electronic device 100 can be put around the arm so as tofit the arm snugly. Note that the cross sections of the boards 111 and112 may have a rectangular shape such as a square-bracket shape.

At least a portion of the board 111 preferably has a light-transmittingproperty. Examples of the board 111 include glass, quartz, plastic, aflexible board, an attachment film including a resin, paper including afibrous material, and a base film. Examples of glass include bariumborosilicate glass, aluminoborosilicate glass, and soda lime glass.Examples of a flexible board, an attachment film, and a base filminclude plastic typified by polyethylene terephthalate (PET),polyethylene naphthalate (PEN), polyether sulfone (PES), andpolytetrafluoroethylene (PTFE); a synthetic resin such as acrylic;polypropylene; polyester; polyvinyl fluoride; polyvinyl chloride;polyamide (such as aramid); polyimide; epoxy; and an inorganic vapordeposition film.

The board 111 may include a first region having a light-transmittingproperty and a second region having a transflective or light-blockingproperty. In an example of the electronic device 100 illustrated in FIG.3A, the board 111 includes a region 164 having a light-transmittingproperty and a region 165 having a light-blocking property.

For the board 112, any of the above materials for the board 111 can beused. Alternatively, for the board 112, a board including metal,stainless steel, or stainless steel foil, a board including tungsten ortungsten foil, paper, a semiconductor (such as a single crystalsemiconductor or a silicon semiconductor), or the like may be used.

For the board 112, a material having higher rigidity than the board 111may be used, for example. For the board 112, for example, a stainlesssteel material may be used. A stainless steel material serves as aprotective material which prevents the display portion 102 and the powerstorage device 103 from being curved excessively or from being twistedand deformed significantly. A stainless steel material only allows achange into a certain shape, i.e., bending in one direction, in puttingthe electronic device on an arm, which improves the reliability.

As illustrated in FIG. 2A or 2B, end portions of the boards 111 and 112may have round shapes. When the end portions of the boards 111 and 112have round shapes, the electronic device can fit a body or the like moresnugly in some cases.

FIG. 3B shows an enlarged view of a region C surrounded by a dashed linein FIG. 2A. An end portion of the board 151 of the display portion 102and an end portion of the power storage device 103 are not fixed to eachother. In wearing the electronic device 100 on an arm or the like, theshape of the board 112 changes in the directions of the arrows 105 inFIG. 2A, and accordingly, the shape of the electronic device 100 alsochanges. Since the end portion of the board 151 and the end portion ofthe power storage device 103 are not fixed to each other, a distance 163between the end portion of the board 151 and the end portion of thepower storage device 103 may change as the shape of the electronicdevice 100 changes.

In contrast, in the case where the display portion 102 and the powerstorage device 103 are fixed to each other, the distance 163 does notnecessarily change as the shape of the electronic device 100 changes.For example, in the case where the end portion of the board 151 and theend portion of the power storage device 103 are fixed to each other, thedistance 163 does not change even when the shape of the electronicdevice 100 is changed, except when the display portion 102 or the powerstorage device 103 is broken or when the display portion 102 or thepower storage device 103 is expanded or contracted depending ontemperature, for example.

As illustrated in FIGS. 4A to 4C, the electronic device 100 may includea board 113 between the display portion 102 and the power storage device103. FIGS. 4A to 4C are different from FIG. 1 in that the board 113 isprovided.

It is preferable that the board 113 be provided between the powerstorage device 103 and the display portion 102 because an external forceapplied to either the power storage device 103 or the display portion102 can be prevented from being easily applied to the other.

For the board 113, any of the materials for the board 112 can be used.As the board 113, for example, a flexible board, an attachment filmincluding a resin, a base film, or the like may be used.

FIG. 4A illustrates a cross section of the electronic device 100. FIG.4B illustrates a cross section which is taken along the dashed-dottedline A-B in FIG. 4A and which is substantially perpendicular to thecross section in FIG. 4A. FIG. 4C illustrates an enlarged view of aregion D surrounded by a dashed line in FIG. 4A. As illustrated in FIG.4C, the board 113 includes a first surface which faces the displayportion, and the first surface includes a region 161 which overlaps withthe display element 152.

Alternatively, for example, the board 113 may include a first surfacewhich faces the board 151 of the display portion 102, and the firstsurface may include a region 161 which faces the display element 152with the board 151 provided therebetween.

A case where the region 161 is fixed to the display portion 102 isconsidered here. In this case, a region 162 of the board 113 on the sideopposite to the region 161 is preferably not fixed to other componentsof the electronic device 100, such as the board 112 and the powerstorage device 103, except the display portion 102 and the board 111.The term “fixed” means, for example, being attached or being fixed bymeans of a fastener such as a screw.

Alternatively, for example, in the case where the region 162 is fixed toother components of the electronic device 100, such as the power storagedevice 103 and the board 112, except the display portion 102 and theboard 111, the region 161 is preferably not fixed to the display portion102.

Alternatively, the board 113 may be fixed to neither the display portion102 nor the power storage device 103.

The board 113 may include a region which is not fixed to the displayportion 102 and one or a plurality of regions which are fixed thereto.Alternatively, there may be a region where the display portion 102 andthe power storage device 103 are fixed to each other with the board 113provided therebetween, for example.

Although the region 161 faces the vicinity of the center of the displayportion 102 in the example of the cross section illustrated in FIG. 4C,the region 161 may exist over a wide region overlapping with the displayelement 152.

Surfaces of the board 113 and the power storage device 103 arepreferably in contact with each other and easily slide on each other.Alternatively, surfaces of the board 113 and the display portion 102 arepreferably in contact with each other and easily slide on each other.The term “easily slide” means, for example, having a low frictioncoefficient or having a small surface unevenness.

As the board 113, a buffer may be used. For example, a materialcontaining bubbles may be used as the buffer. FIGS. 5A and 5B illustratean example of using a bubble buffer (an air cushion) as the board 113.Alternatively, a porous material may be used as the board 113.

FIGS. 6A to 6C illustrate an example where the electronic device 100have two housings. FIG. 6A illustrates a cross section of the electronicdevice 100, and FIG. 6B illustrates a cross section taken along thedashed line A-B in FIG. 6A. In the example illustrated in FIGS. 6A to6C, the electronic device 100 has a housing including the board 111, theboard 112, the sealing portions 121, and the like as a first housing anda housing 126 as a second housing. Inside the first housing of theelectronic device 100, the display portion 102 and the circuit board 107are provided. Inside the housing 126, the power storage device 103 isprovided.

The housing 126 preferably has flexibility. The housing 126 may be asingle component as illustrated in FIGS. 6A to 6C or may be formed byfixing two or more components with a screw or the like. The housing 126can be formed using the same material as the sealing portions 121, forexample.

The vicinities of end portions of the housing 126 are preferably fixedto the first housing with the fasteners 131, for example. In the exampleillustrated in FIGS. 6A to 6C, the housing 126 is fixed to thevicinities of end portions of the board 112 with the fasteners 131.

It is preferable that the housing 126 be at least partly in contact withone surface of the board 112. The housing 126 may be attached to onesurface of the board 112.

Alternatively, the housing 126 may include a first region which is fixedto the first housing and a second region which is not fixed thereto. Inthe case where the board 112 and the housing 126 differ from each otherin how they are bent by an external force, specifically, the degree ofchange in radius of curvature, or the like, the second region which isnot fixed can alleviate the effect of the external force.

Note that a space may be provided between the housing 126 and the board112 of the first housing.

<Example of how to Wear Electronic Device 100>

FIGS. 7A to 7C each illustrate an example of how to wear the electronicdevice 100. In the example of FIG. 7A, the electronic device 100 is wornon an arm (a wrist). In the example of FIG. 7B, the electronic device100 is worn on the upper portion of an arm. In the example of FIG. 7C,the electronic device 100 is an armband device.

The electronic device 100 may be worn on part other than an arm, such asa leg or a finger. Furthermore, the electronic device 100 may be fixedto an arm, a leg, or the like with the use of a belt, for example.Depending on the size of the body part on which the electronic device100 is worn, such as the circumference of an arm, the electronic device100 may be longer than the circumference of the arm. For example, in thecase where the board 112 or the like is longer than the circumference ofan arm in the cross section illustrated in FIG. 2A or the like, theextra regions of the board 112 may overlap each other. In those regions,a region of the board 112 may be in contact with the surface of theboard 111.

The electronic device 100 may include a display region that is long in adirection along the arm as illustrated in FIG. 26. When the length ofthe display region of the electronic device 100 in the direction alongthe arm in FIG. 26 is larger than or equal to, preferably 1.5 or moretimes, the width of the arm in the cross section, the electronic device100 can have a wide display region. On the other hand, when the lengthof the display region in the direction along the arm is smaller than thewidth of the arm in the cross section, the electronic device 100 can belightweight and easily worn.

<Modification Example of Electronic Device 100>

As in an example of the electronic device 100 illustrated in FIG. 8A,the display portion 102 and the power storage device 103 may be arrangedside by side. FIG. 8A differs from FIGS. 2A to 2C in that the powerstorage device 103 is provided beside the display portion 102. When thepower storage device 103 and the display portion 102 are arranged sideby side, the electronic device 100 can be thin, for example. The thinelectronic device 100 can fit a body or the like more snugly in somecases.

As in an example of the electronic device 100 in FIG. 8B, the board 111and the board 112 may have a ring-like cross-sectional shape.

As in an example of the electronic device 100 illustrated in FIGS. 9Aand 9B, the electronic device 100 may include the power storage device103 and power storage devices 106. Here, the power storage device 103preferably has flexibility. As the power storage device 103, forexample, a thin storage battery whose exterior body is formed using alaminate film can be used. The power storage devices 106 do notnecessarily have flexibility. The power storage devices 106 may havedifferent shapes from the power storage device 103. As the power storagedevices 106, for example, a coin-type (or button-type) storage battery,a rectangular storage battery, or a cylindrical storage battery can beused. For example, in the case where the electronic device 100 includesa memory or the like, the power storage devices 106 can be used asstorage batteries for holding data. Furthermore, the power storagedevices 106 can be used as spare storage batteries for the power storagedevice 103. For a coin-type storage battery, Embodiment 3 can bereferred to.

For example, in the cross section of the electronic device 100illustrated in any of FIG. 1, FIGS. 2A to 2D, FIGS. 3A and 3B, FIGS. 4Ato 4C, FIGS. 5A and 5B, FIGS. 6A to 6C, FIGS. 7A to 7C, FIGS. 8A and 8B,and FIGS. 9A and 9B, the radius of curvature of the board 112 may be 10mm or larger, preferably 5 mm or larger. In order that the electronicdevice 100 illustrated in FIG. 1, FIGS. 2A to 2D, FIGS. 3A and 3B, FIGS.4A to 4C, FIGS. 5A and 5B, FIGS. 6A to 6C, FIGS. 7A to 7C, FIGS. 8A and8B, and FIGS. 9A and 9B can be worn on an arm snugly, the radius ofcurvature of the board 112 is preferably 20 mm or larger, morepreferably 15 mm or larger in the cross section of the board 112.

The electronic device 100 preferably has a shape with which more thanhalf of an arm in the cross section can be covered.

<Power Storage Device>

The power storage device 103 preferably has a bent shape. When the powerstorage device 103 has a bent shape, the power storage device 103 can beprovided in the region with a large radius of curvature of the board111. The power storage device 103 preferably has flexibility. The powerstorage device having flexibility includes a thin flexible film as anexterior body and can change its shape along a curved surface portion ofthe region with a large radius of curvature of the board 111. The powerstorage device 103 can change its shape according to a change in theshape of the board 112 when an external force is applied to theelectronic device 100, e.g., in wearing the electronic device 100 on anarm.

A secondary battery, a capacitor, or the like can be used as the powerstorage device 103.

As the secondary battery, a lithium-ion secondary battery can be used.Alternatively, a secondary battery containing an alkali metal (such assodium or potassium) or an alkaline earth metal (such as calcium,strontium, barium, beryllium, or magnesium) instead of lithium may beused. Still alternatively, an air secondary battery using oxygen in airor the like as an active material may be used as the secondary battery.As the air secondary battery, a lithium air battery or the like may beused.

As the capacitor, an electric double-layer capacitor can be used.Alternatively, a redox capacitor can be used as the capacitor. Stillalternatively, a hybrid capacitor such as a lithium-ion capacitor may beused as the capacitor.

In this embodiment, an example of using, as the power storage device 103having flexibility, a thin secondary battery whose exterior bodyincludes a film will be described. FIG. 10 is an external view of thethin secondary battery. FIG. 11A illustrates a cross section taken alongthe dashed-dotted line A1-A2 in FIG. 10, and FIG. 11B illustrates across section taken along the dashed-dotted line B1-B2 in FIG. 10.

The thin secondary battery includes a sheet-like positive electrode 203,a sheet-like negative electrode 206, a separator 207, an electrolyticsolution 208, an exterior body 209 made of a film, a positive electrodelead electrode 510, and a negative electrode lead electrode 511. Theseparator 207 is provided between the positive electrode 203 and thenegative electrode 206 in the exterior body 209. The exterior body 209is filled with the electrolytic solution 208. The positive electrode 203includes a positive electrode current collector 201 and a positiveelectrode active material layer 202. The negative electrode 206 includesa negative electrode current collector 204 and a negative electrodeactive material layer 205.

FIG. 19 illustrates another example of the cross section taken along thedashed-dotted line A1-A2 in FIG. 10. In the example illustrated in FIG.19, the positive electrode 203 includes the positive electrode activematerial layer 202 only on one side of the positive electrode currentcollector 201. Similarly, the negative electrode 206 includes thenegative electrode active material layer 205 only on one side of thenegative electrode current collector 204.

The positive electrode current collector 201 and the negative electrodecurrent collector 204 can each be formed using a highly conductivematerial which is not alloyed with a carrier ion of lithium or the like,such as a metal typified by stainless steel, gold, platinum, zinc, iron,nickel, copper, aluminum, titanium, or tantalum or an alloy thereof.Alternatively, an aluminum alloy to which an element which improves heatresistance, such as silicon, titanium, neodymium, scandium, ormolybdenum, is added can be used. Still alternatively, a metal elementwhich forms silicide by reacting with silicon can be used. Examples ofthe metal element which forms silicide by reacting with silicon includezirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium,molybdenum, tungsten, cobalt, nickel, and the like. The positiveelectrode current collector 201 and the negative electrode currentcollector 204 can each have a foil-like shape, a plate-like shape(sheet-like shape), a net-like shape, a cylindrical shape, a coil shape,a punching-metal shape, an expanded-metal shape, or the like asappropriate. The positive electrode current collector 201 and thenegative electrode current collector 204 each preferably have athickness greater than or equal to 10 μm and less than or equal to 30μm.

The positive electrode active material layer 202 can contain, forexample, a material into and from which carrier ions can be inserted andextracted. As the carrier ions, lithium ions, other alkali metal ions(e.g., sodium ions or potassium ions), alkaline earth metal ions (e.g.,calcium ions, strontium ions, barium ions, beryllium ions, or magnesiumions) can be used.

Examples of the material into and from which lithium ions can beinserted and extracted include lithium-containing materials with anolivine crystal structure, a layered rock-salt crystal structure, and aspinel crystal structure. As the positive electrode active material, acompound such as LiFeO₂, LiCoO₂, LiNiO₂, LiMn₂O₄, V₂O₅, Cr₂O₅, or MnO₂can be used.

Alternatively, a lithium-containing complex phosphate (LiMPO₄ (generalformula) (M is at least one of Fe(II), Mn(II), Co(II), and Ni(II))) canbe used. Typical examples of the general formula LiMPO₄ include LiFePO₄,LiNiPO₄, LiCoPO₄, LiMnPO₄, LiFe_(a)Ni_(b)PO₄, LiFe_(a)Co_(b)PO₄,LiFe_(a)Mn_(b)PO₄, LiNi_(a)CO_(b)PO₄, LiNi_(a)Mn_(b)PO₄ (a+b≦1, 0<a<1,and 0<b<1), LiFe_(c)Ni_(d)Co_(e)PO₄, LiFe_(c)Ni_(d)Mn_(e)PO₄,LiNi_(c)Co_(d)Mn_(e)PO₄ (c+d+e≦1, 0<c<1, 0<d<1, and 0<e<1), andLiFe_(f)Ni_(g)Co_(h)Mn_(i)PO₄ (f+g+h+i≦1, 0<f<1, 0<g<1, 0<h<1, and0<i<1).

LiFePO₄ is particularly preferable because it properly has propertiesnecessary for the positive electrode active material, such as safety,stability, high capacity density, high potential, and the existence oflithium ions which can be extracted in initial oxidation (charging).

Examples of the lithium-containing material with a layered rock-saltcrystal structure include a lithium-containing material such as lithiumcobalt oxide (LiCoO₂), LiNiO₂, LiMnO₂, or Li₂MnO₃; an NiCo-basedlithium-containing material (a general formula thereof isLiNi_(x)Co_(1−x)O₂ (0<x<1)) such as LiNi_(0.8)Co_(0.2)O₂; an NiMn-basedlithium-containing material (a general formula thereof isLiNi_(x)Mn_(1−x)O₂ (0<x<1)) such as LiNi_(0.5)Mn_(0.5)O₂; and anNiMnCo-based lithium-containing material (also referred to as NMC, and ageneral formula thereof is LiNi_(x)Mn_(y)Co_(1−x−y)O₂ (x>0, y>0, x+y<1))such as LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂. The examples further includeLi(Ni_(0.8)Co_(0.15)Al_(0.05))O₂ and Li₂MnO₃—LiMO₂ (M=Co, Ni, or Mn).

Examples of the lithium-containing material with a spinel crystalstructure include LiMn₂O₄, Li_(1+x)Mn_(2−x)O₄, LiMn_(2−x)Al_(x)O₄(0<x<2), and LiMn_(1.5)Ni_(0.5)O₄.

It is preferable to add a small amount of lithium nickel oxide (LiNiO₂or LiNi_(1−x)Mn_(x)O₂ (M=Co or Al, for example)) to a lithium-containingmaterial with a spinel crystal structure which contains manganese suchas LiMn₂O₄ because advantages such as inhibition of the dissolution ofmanganese and the decomposition of an electrolytic solution can beobtained.

Alternatively, a lithium-containing material represented by a generalformula, Li_((2-j))MSiO₄ (M is one or more of Fe(II), Mn(II), Co(II),and Ni(II), 0≦j≦2), can be used as the positive electrode activematerial. Typical examples of Li_((2−j))MSiO₄ (general formula) includelithium compounds such as Li_((2−j))FeSiO₄, Li_((2−j))NiSiO₄,Li_((2−j))CoSiO₄, Li_((2−j))MnSiO₄, Li_((2−j))Fe_(k)Ni_(l)SiO₄,Li_((2−j))Fe_(k)Co_(l)SiO₄, Li_((2−j))Fe_(k)Mn_(l)SiO₄,Li_((2−j))Ni_(k)Co_(l)SiO₄, Li_((2−j))Ni_(k)Mn_(l)SiO₄ (k+l≦1, 0<k<1,and 0<l<1), Li_((2−j))Fe_(m)Ni_(n)Co_(q)SiO₄,Li_((2−j))Fe_(m)Ni_(n)Mn_(q)SiO₄, Li_((2−j))Ni_(m)Co_(n)Mn_(q)SiO₄(m+n+q≦1, 0<m<1, 0<n<1, and 0<q<1), andLi_((2−j))Fe_(r)Ni_(s)Co_(t)Mn_(u)SiO₄ (r+s+t+u≦1, 0<r<1, 0<s<1, 0<t<1,and 0<u<1).

Still alternatively, a NASICON compound represented by a generalformula, A_(x)M₂(XO₄)₃ (A=Li, Na, or Mg, M=Fe, Mn, Ti, V, Nb, or Al, andX=S, P, Mo, W, As, or Si), can be used as the positive electrode activematerial. Examples of the NASICON compound include Fe₂(MnO₄)₃,Fe₂(SO₄)₃, and Li₃Fe₂(PO₄)₃. Still further alternatively, a compoundrepresented by a general formula, Li₂MPO₄F, Li₂MP₂O₇, or Li₅MO₄ (M=Fe orMn), a perovskite fluoride such as NaF₃ or FeF₃, a metal chalcogenide (asulfide, a selenide, or a telluride) such as TiS₂ or MoS₂, a materialwith an inverse spinel crystal structure such as LiMVO₄, a vanadiumoxide (e.g., V₂O₅, V₆O₁₃, or LiV₃O₈), a manganese oxide, or an organicsulfur compound can be used as the positive electrode active material,for example.

As the positive electrode active material, a sodium-containing materialmay be used. For example, NaMn₂O₄, NaNiO₂, NaCoO₂, NaFeO₂,NaNi_(0.5)Mn_(0.5)O₂, NaCrO₂, or NaFeO₂ can be used. Alternatively, afluorophosphate such as Na₂FePO₄F, Na₂VPO₄F, Na₂MnPO₄F, Na₂CoPO₄F, orNa₂NiPO₄F can be used. Still alternatively, a borate such as NaFeBO₄ orNa₃Fe₂(BO₄)₃ can be used.

Any of such substances to which a rare earth element is added may beused as the positive electrode active material. The rare earth elementare Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, andLu. A positive electrode active material to which one or more of theelements are added can be used.

The positive electrode active material layer 202 may further include abinder for increasing adhesion of active materials, a conductiveadditive for increasing the conductivity of the positive electrodeactive material layer 202, and the like in addition to theabove-described positive electrode active materials.

A material with which a metal to be carrier ions can be dissolved andprecipitated or a material into and from which carrier ions can beinserted and extracted can be used for the negative electrode activematerial layer 205. For example, a lithium metal, a carbon-basedmaterial, or an alloy-based material can be used. Examples of the metalto be the carrier ions include lithium, other alkali metals (e.g.,sodium and potassium), alkaline earth metals (e.g., calcium, strontium,barium, beryllium, and magnesium), and the like.

The lithium metal is preferable because of its low redox potential(3.045 V lower than that of a standard hydrogen electrode) and highspecific capacity per unit weight and per unit volume (3860 mAh/g and2062 mAh/cm³).

Examples of the carbon-based material include graphite, graphitizingcarbon (soft carbon), non-graphitizing carbon (hard carbon), a carbonnanotube, graphene, carbon black, and the like.

Examples of the graphite include artificial graphite such as meso-carbonmicrobeads (MCMB), coke-based artificial graphite, or pitch-basedartificial graphite and natural graphite such as spherical naturalgraphite.

Graphite has a low potential substantially equal to that of a lithiummetal (lower than or equal to 0.3 V vs. Li/Li⁺) when lithium ions areintercalated into the graphite (while a lithium-graphite intercalationcompound is formed). For this reason, a lithium-ion secondary batterycan have a high operating voltage. In addition, graphite is preferablebecause of its advantages such as relatively high capacity per unitvolume, small volume expansion, low cost, and safety greater than thatof a lithium metal.

For the negative electrode active material, an alloy-based material canbe used. The term “alloy-based material” refers to a material whichenables charge-discharge reactions by an alloying reaction and adealloying reaction with a metal to be carrier ions. For example, in thecase where carrier ions are lithium ions, a material including at leastone of Mg, Ca, Al, Si, Ge, Sn, Pb, Sb, As, Bi, Ag, Au, Zn, Cd, Hg, In,and the like can be used as the alloy-based material. Such elements havehigher capacity than carbon. In particular, silicon has a significantlyhigh theoretical capacity of 4200 mAh/g. For this reason, silicon ispreferably used for the negative electrode active material. Amongcompounds using such elements, a material that enables charge-dischargereactions by forming a bond with lithium may also be referred to as analloy-based material. Examples include SiO, Mg₂Si, Mg₂Ge, SnO, SnO₂,Mg₂Sn, SnS₂, V₂Sn₃, FeSn₂, CoSn₂, Ni₃Sn₂, Cu₆Sn₅, Ag₃Sn, Ag₃Sb, Ni₂MnSb,CeSb₃, LaSn₃, La₃Co₂Sn₇, CoSb₃, InSb, SbSn, and the like.

Alternatively, for the negative electrode active material, an oxide suchas titanium dioxide (TiO₂), lithium titanium oxide (Li₄Ti₅O₁₂),lithium-graphite intercalation compound (Li_(x)C₆), niobium pentoxide(Nb₂O₅), tungsten oxide (WO₂), or molybdenum oxide (MoO₂) can be used.

Still alternatively, for the negative electrode active material,Li_(3−x)M_(x)N (M=Co, Ni, or Cu) with a Li₃N structure, which is anitride containing lithium and a transition metal, can be used. Forexample, Li_(2.6)Co_(0.4)N₃ is preferable because of high charge anddischarge capacity (900 mAh/g and 1890 mAh/cm³).

A nitride containing lithium and a transition metal is preferably used,in which case lithium ions are contained in the negative electrodeactive material and thus the negative electrode active material can beused in combination with a material for a positive electrode activematerial which does not contain lithium ions, such as V₂O₅ or Cr₃O₈. Inthe case of using a material containing lithium ions as a positiveelectrode active material, the nitride containing lithium and atransition metal can be used for the negative electrode active materialby extracting the lithium ions contained in the positive electrodeactive material in advance.

Alternatively, a material which causes a conversion reaction can be usedfor the negative electrode active material. For example, a transitionmetal oxide which does not cause an alloy reaction with lithium, such ascobalt oxide (CoO), nickel oxide (NiO), or iron oxide (FeO), may beused. Other examples of the material which causes a conversion reactioninclude oxides such as Fe₂O₃, CuO, Cu₂O, RuO₂, and Cr₂O₃, sulfides suchas CoS_(0.89), NiS, and CuS, nitrides such as Zn₃N₂, Cu₃N, and Ge₃N₄,phosphides such as NiP₂, FeP₂, and CoP₃, and fluorides such as FeF₃ andBiF₃. Note that any of the fluorides can be used as a positive electrodeactive material because of its high potential.

The negative electrode active material layer 205 may further include abinder for increasing adhesion of active materials, a conductiveadditive for increasing the conductivity of the negative electrodeactive material layer 205, and the like in addition to theabove-described negative electrode active materials.

As an electrolyte in the electrolytic solution 208, a material which hascarrier ion mobility and contains lithium ions serving as carrier ionsis used. Typical examples of the electrolyte are lithium salts such asLiPF₆, LiClO₄, Li(FSO₂)₂N, LiAsF₆, LiBF₄, LiCF₃SO₃, Li(CF₃SO₂)₂N, andLi(C₂F₅SO₂)₂N. One of these electrolytes may be used alone, or two ormore of them may be used in an appropriate combination and in anappropriate ratio. In order to stabilize a reaction product, a smallamount (1 wt %) of vinylene carbonate (VC) may be added to theelectrolytic solution so that the decomposition amount of theelectrolytic solution is further reduced. As an electrolyte containingsodium ions, NaPF₆, NaN(SO₂CF₃)₂, NaClO₄, NaBF₄, CF₃SO₃Na, and NaAsF₆,or the like may be used.

As a solvent of the electrolytic solution 208, a material in whichcarrier ions can transfer is used. As the solvent of the electrolyticsolution, an aprotic organic solvent is preferably used. Typicalexamples of aprotic organic solvents include ethylene carbonate (EC),propylene carbonate, dimethyl carbonate, diethyl carbonate (DEC),γ-butyrolactone, acetonitrile, dimethoxyethane, tetrahydrofuran, and thelike, and one or more of these materials can be used. When a gelledhigh-molecular material is used as the solvent of the electrolyticsolution, safety against liquid leakage and the like is improved.Furthermore, the storage battery can be thinner and more lightweight.Typical examples of gelled high-molecular materials include a siliconegel, an acrylic gel, an acrylonitrile gel, a polyethylene oxide-basedgel, a polypropylene oxide-based gel, a gel of a fluorine-based polymer,and the like. Alternatively, the use of one or more of ionic liquids(room temperature molten salts) which have features of non-flammabilityand non-volatility as a solvent of the electrolytic solution can preventthe storage battery from exploding or catching fire even when thestorage battery internally shorts out or the internal temperatureincreases owing to overcharging or the like.

As the separator 207, an insulator can be used. For example, cellulose(paper) can be used. Alternatively, a polymer, such as polypropylene andpolyethylene, with pores can be used.

In the secondary battery, a thin flexible film (such as a laminate film)is used as an exterior body. The laminate film refers to a stacked filmof a base film and an adhesive synthetic resin film, or a stacked filmof two or more kinds of films. For the base film, polyester such as PETand PBT, polyamide such as nylon 6 or nylon 66, an inorganic film formedby evaporation, or paper may be used. For the adhesive synthetic resinfilm, polyolefin such as PE and PP, an acrylic-based synthetic resin, anepoxy-based synthetic resin, or the like may be used. An object islaminated with the laminate film by thermocompression bonding using alaminating apparatus. Note that an anchor coat agent is preferablyapplied as pretreatment for the laminating step so that the adhesionbetween the laminate film and the object can be increased. As the anchorcoat agent, an isocyanate-based material or the like may be used.

Embodiment 4 can be referred to for a method for manufacturing the thinsecondary battery whose exterior body includes a film.

<Method for Manufacturing Display Portion>

An example of a method for manufacturing the display portion 102 will bedescribed below.

The display portion 102 has flexibility. The display portion 102includes the display element 152 over the board 151 having flexibility.

Examples of methods for manufacturing the display element 152 over theboard 151 having flexibility include a method in which the displayelement 152 is directly formed over the board 151 having flexibility; amethod in which a layer including the display element 152 is formed overa rigid substrate such as a glass substrate, the substrate is removed byetching, polishing, or the like, and then the layer including thedisplay element 152 and the board 151 having flexibility are attached toeach other; a method in which a separation layer is provided over arigid substrate such as a glass substrate, a layer including the displayelement 152 is formed thereover, the rigid substrate and the layerincluding the display element 152 are separated from each other usingthe separation layer, and then the layer including the display element152 and the board 151 having flexibility are attached to each other; andthe like.

In this embodiment, a manufacturing method which allows heat treatmentto be performed at 400° C. or higher and which can improve thereliability of the display element, i.e., a technique in which aseparation layer is provided over a rigid substrate such as a glasssubstrate as disclosed in Japanese Published Patent Application No.2003-174153, is used so that the display portion 102 can be anactive-matrix display device capable of displaying high-resolutionimages.

The technique disclosed in Japanese Published Patent Application No.2003-174153 enables transistors including polysilicon in active layersor transistors including oxide semiconductor layers to be provided overa flexible substrate or film. These transistors are used as switchingelements, and electroluminescent (EL) elements are provided.

In a common structure of the EL element, a layer including alight-emitting organic compound or inorganic compound (hereinafterreferred to as a light-emitting layer) is provided between a pair ofelectrodes, and when a voltage is applied to the element, electrons andholes are separately injected and transported from the pair ofelectrodes to the light-emitting layer. When those carriers (electronsand holes) recombine, an excited state of the light-emitting organiccompound or inorganic compound is formed, and when the light-emittingorganic compound or inorganic compound returns to a ground state, lightis emitted.

Further, kinds of excited state that can be formed by an organiccompound are a singlet excited state and a triplet excited state. Lightemission in the case of a singlet excited state is referred to asfluorescence, and light emission in the case of a triplet excited stateis referred to as phosphorescence.

Such a light-emitting element is usually formed of thin films which havea thickness of submicrons to several microns. Therefore, they can bemanufactured to be thin and light, which is a large advantage. Further,such light-emitting elements also have an advantage in that the periodof time from when the carriers are injected until light is emitted ismicroseconds at the most, so they have a very high response speed.Moreover, because sufficient light emission can be obtained with adirect current voltage of several to several tens of volts, powerconsumption is also relatively low.

EL elements have a wider viewing angle than liquid crystal elements andare preferable as display elements in the display portion 102 when adisplay region has a curved surface. In addition, EL elements arepreferable as display elements in the display portion 102 in that unlikeliquid crystal elements, EL elements do not require a backlight, whichmakes it possible to reduce power consumption, the number of components,and the total thickness.

Note that methods for manufacturing the display element 152 over theboard 151 having flexibility are not limited to the method mentionedabove (Japanese Published Patent Application No. 2003-174153). Methodsand materials for manufacturing EL elements may be known methods andmaterials and are therefore not described here.

The display device used as the display portion 102 may only be capableof simply displaying single-color images or displaying numbers.Therefore, a passive-matrix display device may be used, in which casethe display element 152 may be manufactured over the board 151 havingflexibility using a method other than the technique disclosed inJapanese Published Patent Application No. 2003-174153.

The display portion 102 obtained by the above method is attached to thepower storage device 103, and the power storage device 103 and thedisplay portion 102 are electrically connected to each other.Furthermore, a metal cover, a plastic cover, or a rubber cover may beprovided over a portion other than the display portion 102 to improvethe appearance of the electronic device 100.

In the case where the electronic device 100 is provided with the displayportion 102, the screen size is not particularly limited. For example,the screen size of the display portion 102 may be smaller than or equalto the size of the board 112. For example, in the case where theelectronic device is worn on an arm, the maximum screen size is theproduct of an arm girth of 23 cm and a wrist-to-elbow length because thegirth of an adult arm near a wrist is 18 cm±5 cm. The wrist-to-elbowlength of an adult is shorter than or equal to a feet (30.48 cm); thus,the maximum screen size of the display portion in the electronic device100 that is worn on an arm is 23 cm×30.48 cm, which is the size of theboard 112 in the form of a cylinder tube, for example. Note that thescreen size here does not refer to the size in a curved state but refersto the size in a flat state. A plurality of display portions may beprovided in one electronic device; for example, a second display portionsmaller than a first display portion may be included in an electronicdevice. The dimension of the board 112 is preferably set larger than thescreen size of the display portion. In the case of using EL elements,when the display portion is of such a screen size that it can bedisposed over a support structure body, the sum of the weights of thedisplay panel and the FPC can be more than or equal to 1 g and less than10 g.

The thickness of the thinnest portion of the electronic device 100provided with the display portion 102 can be less than or equal to 5 mm.The thickness of the thickest portion of the electronic device 100,which is a portion where the display portion 102 and the FPC areconnected to each other, can be less than 1 cm.

The total weight of the electronic device 100 can be less than 100 g.

The electronic device 100 can be put on an arm because part of thesupport structure body can be moved in the direction of the arrows 105as illustrated in the cross-sectional views of FIG. 2A and the like. Theelectronic device 100 has a total weight less than 100 g, preferablyless than or equal to 50 g and a small maximum thickness less than orequal to 1 cm; thus, a lightweight electronic device can be provided.

For example, in this specification and the like, a display element, adisplay device which is a device including a display element, alight-emitting element, and a light-emitting device which is a deviceincluding a light-emitting element can employ a variety of modes or caninclude a variety of elements. The display element, the display device,the light-emitting element, or the light-emitting device includes atleast one of an electroluminescent (EL) element (e.g., an EL elementincluding organic and inorganic materials, an organic EL element, or aninorganic EL element), an LED (e.g., a white LED, a red LED, a greenLED, or a blue LED), a transistor (a transistor that emits lightdepending on current), an electron emitter, a liquid crystal element,electronic ink, an electrophoretic element, a grating light valve (GLV),a plasma display panel (PDP), a display element using micro electromechanical systems (MEMS), a digital micromirror device (DMD), a digitalmicro shutter (DMS), MIRASOL (registered trademark), an interferometricmodulator display (IMOD) element, a MEMS shutter display element, anoptical-interference-type MEMS display element, an electrowettingelement, a piezoelectric ceramic display, a display element including acarbon nanotube, and the like. In addition to that, display media whosecontrast, luminance, reflectivity, transmittance, or the like is changedby electrical or magnetic effect may be included. Examples of displaydevices including EL elements include an EL display. Display devicesincluding electron emitters include a field emission display (FED), anSED-type flat panel display (SED: surface-conduction electron-emitterdisplay), and the like. Examples of display devices including liquidcrystal elements include a liquid crystal display (e.g., a transmissiveliquid crystal display, a transflective liquid crystal display, areflective liquid crystal display, a direct-view liquid crystal display,or a projection liquid crystal display). Examples of a display deviceincluding electronic ink, Electronic Liquid Powder (registeredtrademark), or an electrophoretic element include electronic paper. Inthe case of a transflective liquid crystal display or a reflectiveliquid crystal display, some or all of pixel electrodes function asreflective electrodes. For example, some or all of pixel electrodes areformed to contain aluminum, silver, or the like. In such a case, amemory circuit such as an SRAM can be provided under the reflectiveelectrodes, leading to lower power consumption. Note that in the case ofusing an LED, graphene or graphite may be provided under an electrode ora nitride semiconductor of the LED. Graphene or graphite may be amultilayer film in which a plurality of layers are stacked. Whengraphene or graphite is provided in this manner, a nitridesemiconductor, for example, an n-type GaN semiconductor layer includingcrystals can be easily formed thereover. Furthermore, a p-type GaNsemiconductor layer including crystals or the like can be providedthereover, and thus the LED can be formed. Note that an AlN layer may beprovided between the n-type GaN semiconductor layer including crystalsand graphene or graphite. The GaN semiconductor layers included in theLED may be formed by MOCVD. Note that when the graphene is provided, theGaN semiconductor layers included in the LED can also be formed by asputtering method.

In addition to the display device, the electronic device of oneembodiment of the present invention may include another semiconductorcircuit, e.g., a control circuit for preventing overcharge, an imagingelement, a sensor such as a gyroscope sensor or an acceleration sensor,a touch panel, or the like. Furthermore, a sensor or the like formeasuring a pulse, a surface temperature, a blood oxygen level, or thelike by touch on part of a human body may be included. For example, whenan imaging element is included in addition to the display device, ataken image can be displayed on the display device. When a sensor suchas a gyroscope sensor or an acceleration sensor is included, thearm-worn electronic device can be powered on or off depending on theorientation or movement thereof to reduce power consumption. When atouch panel is included, the electronic device can be operated orinformation can be input by touching a predetermined position of thetouch panel. When a memory and a CPU are included in addition to thedisplay device in the above structure, a wearable computer can beobtained.

When the electronic device of one embodiment of the present invention isused as the display portion of the arm-worn electronic device togetherwith a display portion of a conventional portable information terminal,the electronic device of one embodiment of the present invention can beused as a sub-display.

This embodiment can be implemented in appropriate combination with anyof the other embodiments.

Embodiment 2

In this embodiment, an example of a display device that can be used inan electronic device of one embodiment of the present invention will bedescribed.

[Top View of Display Device]

FIG. 20 is a top view of an example of a display device. A displaydevice 700 illustrated in FIG. 20 includes a pixel portion 702 providedover a first substrate 701; a source driver circuit portion 704 and agate driver circuit portion 706 provided over the first substrate 701; asealant 712 provided to surround the pixel portion 702, the sourcedriver circuit portion 704, and the gate driver circuit portion 706; anda second substrate 705 provided to face the first substrate 701. Thefirst substrate 701 and the second substrate 705 are sealed with thesealant 712. That is, the pixel portion 702, the source driver circuitportion 704, and the gate driver circuit portion 706 are sealed with thefirst substrate 701, the sealant 712, and the second substrate 705.Although not illustrated in FIG. 20, a display element is providedbetween the first substrate 701 and the second substrate 705.

In the display device 700, a flexible printed circuit (FPC) terminalportion 708 electrically connected to the pixel portion 702, the sourcedriver circuit portion 704, and the gate driver circuit portion 706 isprovided in a region different from the region which is surrounded bythe sealant 712 and positioned over the first substrate 701.Furthermore, an FPC 716 is connected to the FPC terminal portion 708,and a variety of signals and the like are supplied to the pixel portion702, the source driver circuit portion 704, and the gate driver circuitportion 706 through the FPC 716. Furthermore, a signal line 710 isconnected to the pixel portion 702, the source driver circuit portion704, the gate driver circuit portion 706, and the FPC terminal portion708. A variety of signals and the like are applied to the pixel portion702, the source driver circuit portion 704, the gate driver circuitportion 706, and the FPC terminal portion 708 via the signal line 710from the FPC 716.

A plurality of gate driver circuit portions 706 may be provided in thedisplay device 700. An example of the display device 700 in which thesource driver circuit portion 704 and the gate driver circuit portion706 are formed over the first substrate 701 where the pixel portion 702is also formed is described; however, the structure is not limitedthereto. For example, only the gate driver circuit portion 706 may beformed over the first substrate 701 or only the source driver circuitportion 704 may be formed over the first substrate 701. In this case, asubstrate where a source driver circuit, a gate driver circuit, or thelike is formed (e.g., a driver-circuit substrate formed using asingle-crystal semiconductor film or a polycrystalline semiconductorfilm) may be mounted on the first substrate 701. Note that there is noparticular limitation on the method of connecting a separately prepareddriver circuit substrate, and a chip on glass (COG) method, a wirebonding method, or the like can be used.

The pixel portion 702, the source driver circuit portion 704, and thegate driver circuit portion 706 included in the display device 700include a wiring portion or a plurality of transistors. As the wiringportion or the plurality of transistors, any of the semiconductordevices of embodiments of the present invention can be used.

The display device 700 can include any of a variety of elements.Examples of the elements include a liquid crystal element, anelectroluminescence (EL) element (e.g., an EL element including organicand inorganic materials, an organic EL element, or an inorganic ELelement), an LED (e.g., a white LED, a red LED, a green LED, or a blueLED), a transistor (a transistor that emits light depending on current),an electron emitter, electronic ink, an electrophoretic element, a GLV,a PDP, a display element using MEMS, a DMD, a DMS, MIRASOL (registeredtrademark), an IMOD element, a MEMS shutter display element, anoptical-interference-type MEMS display element, an electrowettingelement, a piezoelectric ceramic display, and a display elementincluding a carbon nanotube, which are display media whose contrast,luminance, reflectance, transmittance, or the like is changed byelectrical or magnetic action.

As a display method in the display device 700, a progressive method, aninterlace method, or the like can be employed. Furthermore, colorelements controlled in a pixel at the time of color display are notlimited to three colors of R, G, and B (R, G, and B correspond to red,green, and blue, respectively). For example, four pixels of an R pixel,a G pixel, a B pixel, and a W (white) pixel may be included.Alternatively, a color element may be composed of two colors among R, G,and B as in PenTile layout. The two colors may differ among colorelements. Alternatively, one or more colors of yellow, cyan, magenta,and the like may be added to RGB. The size of a display region may bedifferent between respective dots of the color components. Embodimentsof the disclosed invention are not limited to a display device for colordisplay; the disclosed invention can also be applied to a display devicefor monochrome display.

A coloring layer (also referred to as a color filter) may be used inorder to obtain a full-color display device in which white light (W) fora backlight (e.g., an organic EL element, an inorganic EL element, anLED, or a fluorescent lamp) is used. As the coloring layer, red (R),green (G), blue (B), yellow (Y), or the like may be combined asappropriate, for example. With the use of the coloring layer, highercolor reproducibility can be obtained than in the case without thecoloring layer. In this case, by providing a region with the coloringlayer and a region without the coloring layer, white light in the regionwithout the coloring layer may be directly utilized for display. Bypartly providing the region without the coloring layer, a decrease inluminance due to the coloring layer can be suppressed, and approximately20% to 30% of power consumption can be reduced in some cases when animage is displayed brightly. Note that in the case where full-colordisplay is performed using a self-luminous element such as an organic ELelement or an inorganic EL element, elements may emit light of theirrespective colors R, G, B, Y, and white (W). By using a self-luminouselement, power consumption can be further reduced as compared to thecase of using the coloring layer in some cases.

In this embodiment, structures including a liquid crystal element and anEL element as display elements will be described with reference to FIGS.21 to 24. Note that FIG. 21 is a cross-sectional view along thedashed-dotted line Q-R shown in FIG. 20 and shows a structure includinga liquid crystal element as a display element, whereas FIG. 24 is across-sectional view along the dashed-dotted line Q-R shown in FIG. 20and shows a structure including an EL element as a display element.

Common portions between FIG. 21 and FIG. 24 are described first, andthen different portions are described.

[Common Portions in Display Devices]

The display device 700 illustrated in each of FIGS. 21 and 24 includes alead wiring portion 711, the pixel portion 702, the source drivercircuit portion 704, and the FPC terminal portion 708. The lead wiringportion 711 includes the signal line 710. The pixel portion 702 includesa transistor 750 and a capacitor 790 (a capacitor 790 a or a capacitor790 b). The source driver circuit portion 704 includes a transistor 752.

The signal line 710 is formed through the same process as conductivefilms functioning as a source electrode and a drain electrode of thetransistor 750 or 752. Note that the signal line 710 may be formed usinga conductive film which is formed through a different process from thesource electrode and the drain electrode of the transistor 750 or 752,e.g., a conductive film functioning as a gate electrode. In the casewhere the signal line 710 is formed using a material containing a copperelement, signal delay or the like due to wiring resistance is reduced,which enables display on a large screen.

Any of a variety of transistors can be used as the transistors 750 and752. The transistors 750 and 752 each include a gate electrode 721, asemiconductor layer 722, and electrodes 723 and 724. In addition, aninsulating film is provided between the semiconductor layer 722 and thegate electrode 721.

There is no particular limitation on the structure of the transistors,such as the transistor 750 and the transistor 752, in the light-emittingdevice 700. For example, a forward staggered transistor or an invertedstaggered transistor may be used. A top-gate transistor or a bottom-gatetransistor may be used. There is no particular limitation on asemiconductor material used for the transistors; for example, silicon,germanium, silicon carbide, or gallium nitride can be used.Alternatively, an oxide semiconductor containing at least one of indium,gallium, and zinc, such as an In—Ga—Zn-based metal oxide, may be used.

There is no particular limitation on the crystallinity of asemiconductor material used for the transistors, and an amorphoussemiconductor or a semiconductor having crystallinity (amicrocrystalline semiconductor, a polycrystalline semiconductor, asingle-crystal semiconductor, or a semiconductor partly includingcrystal regions) may be used. It is preferable that a semiconductorhaving crystallinity be used, in which case deterioration of thetransistor characteristics can be suppressed.

Here, an oxide semiconductor is preferably used for semiconductordevices such as transistors used for pixels, driver circuits, touchsensors, and the like. In particular, an oxide semiconductor having awider band gap than silicon is preferably used. A semiconductor materialhaving a wider band gap and a lower carrier density than silicon ispreferably used because off-state current of the transistor can bereduced.

For example, the oxide semiconductor preferably contains at least indium(In) or zinc (Zn). More preferably, the oxide semiconductor contains anoxide represented by an In-M-Zn-based oxide (M is a metal which is anyone of Al, Ti, Ga, Ge, Y, Zr, Sn, La, Ce, and Hf).

As the semiconductor layer, it is particularly preferable to use anoxide semiconductor film including a plurality of crystal parts whosec-axes are aligned perpendicular to a surface on which the semiconductorlayer is formed or the top surface of the semiconductor layer and inwhich the adjacent crystal parts have no grain boundary.

There is no grain boundary in such an oxide semiconductor; therefore,generation of a crack in an oxide semiconductor film which is caused bystress when a display panel is bent is prevented. Therefore, such anoxide semiconductor can be preferably used for a flexible display panelwhich is used in a bent state, or the like.

The use of such materials for the semiconductor layer makes it possibleto provide a highly reliable transistor in which a change in theelectrical characteristics is suppressed.

Charge accumulated in a capacitor through a transistor can be held for along time because of the low off-state current of the transistor. Whensuch a transistor is used for a pixel, operation of a driver circuit canbe stopped while a gray scale of an image displayed in each displayregion is maintained. As a result, an electronic device with anextremely low power consumption can be obtained.

For stable characteristics of the transistor, a base film is preferablyprovided. The base film can be formed with an inorganic insulating filmsuch as a silicon oxide film, a silicon nitride film, a siliconoxynitride film, or a silicon nitride oxide film to have a single-layerstructure or a stacked-layer structure. The base film can be formed by asputtering method, a chemical vapor deposition (CVD) method (e.g., aplasma CVD method, a thermal CVD method, and a metal organic CVD (MOCVD)method), an atomic layer deposition (ALD) method, a coating method, aprinting method, or the like. Note that the base film is not necessarilyprovided.

The FPC terminal portion 708 includes a connection electrode 760, ananisotropic conductive film 780, and the FPC 716. Note that theconnection electrode 760 is formed through the same process as theconductive films functioning as the source electrode and the drainelectrode of the transistor 750 or 752. The connection electrode 760 iselectrically connected to a terminal included in the FPC 716 through theanisotropic conductive film 780.

For example, a glass substrate can be used as the first substrate 701and the second substrate 705. As the glass substrate, a glass substratehaving a curved surface may be used.

A substrate having flexibility may be used as the first substrate 701and the second substrate 705. Examples of the substrate havingflexibility include a plastic substrate. The substrate havingflexibility may be attached to a board or the like.

A display device having flexibility can be manufactured with the use ofthe substrate having flexibility. When the display device hasflexibility, the display device can be attached to a curved surface oran irregular shape, whereby a variety of applications are achieved.

For example, the substrate having flexibility such as a plasticsubstrate is used, whereby the display device can be thinner and morelightweight. In addition, the display device in which the substratehaving flexibility such as a plastic substrate is used is hardly broken,and can withstand impacts well when dropped, for example.

Furthermore, a light-blocking film 738 functioning as a black matrix, acoloring film 736 functioning as a color filter, and an insulating film734 in contact with the light-blocking film 738 and the coloring film736 are provided on the second substrate 705 side.

A structure 778 is provided between the first substrate 701 and thesecond substrate 705. The structure 778 is a columnar spacer obtained byselective etching of an insulating film and is provided to control thedistance (cell gap) between the first substrate 701 and the secondsubstrate 705. Note that a spherical spacer may be used as the structure778. Although the example in which the structure 778 is provided on thesecond substrate 705 side is illustrated in FIG. 21, one embodiment ofthe present invention is not limited thereto. For example, asillustrated in FIG. 24, the structure 778 may be provided on the firstsubstrate 701 side, or both the first substrate 701 and the secondsubstrate 705 may be provided with the structure 778.

In FIG. 21 and FIG. 24, insulating films 764, 766, and 768 are providedover the transistor 750, the transistor 752, and the capacitor 790.

The display device 700 may include a protective film 799. The protectivefilm 799 is preferably formed uniformly. It is preferable to use an ALDmethod as an example of a method for forming the protective film 799.The protective film 799 has a function of protecting the display elementand the transistors, for example. A protective film such as theprotective film 799 may have another function, for example. Thus, theprotective film such as the protective film 799 may be simply referredto as a film. For example, the protective film such as the protectivefilm 799 may be referred to as a first film, a second film, or the like.

In the case where an oxide semiconductor is used for the semiconductorlayer of the transistor 750 or 752, an insulating film having a blockingeffect against oxygen, hydrogen, water, and the like is preferablyprovided as the insulating film 768 because it is possible to preventoutward diffusion of oxygen from the semiconductor layer of thetransistor 750 or 752 and entry of hydrogen, water, and the like intothe semiconductor layer from the outside. The insulating film 768 mayfunction as a protective film.

The insulating film 768 can be formed using, for example, an insulatingfilm containing at least one of aluminum oxide, magnesium oxide, siliconoxide, silicon oxynitride, silicon nitride oxide, silicon nitride,gallium oxide, germanium oxide, yttrium oxide, zirconium oxide,lanthanum oxide, neodymium oxide, hafnium oxide, and tantalum oxide. Theinsulating film 768 may be a stack of any of the above materials. Theinsulating film 768 may contain lanthanum (La), nitrogen, zirconium(Zr), or the like as an impurity.

[Structure Example of Display Device Using Liquid Crystal Element asDisplay Element]

The display device 700 illustrated in FIG. 21 includes the capacitor 790a. The capacitor 790 a has a structure in which a dielectric is providedbetween a pair of electrodes.

In addition, the display device 700 illustrated in FIG. 21 includes aliquid crystal element 775. The liquid crystal element 775 includes aconductive film 772, a conductive film 774, and a liquid crystal layer776. The conductive film 774 is provided on the second substrate 705side and functions as a counter electrode. The display device 700 inFIG. 21 is capable of displaying an image in such a manner that lighttransmission or non-transmission is controlled by change in thealignment state of the liquid crystal layer 776 depending on a voltageapplied between the conductive film 772 and the conductive film 774.

The conductive film 772 is connected to the conductive film functioningas the source electrode or the drain electrode included in thetransistor 750. The conductive film 772 is formed over the insulatingfilm 768 to function as a pixel electrode, i.e., one electrode of thedisplay element.

The conductive film 772 can be formed using a light-transmittingconductive material such as indium tin oxide, indium oxide containingtungsten oxide, indium zinc oxide containing tungsten oxide, indiumoxide containing titanium oxide, indium tin oxide containing titaniumoxide, indium zinc oxide, or indium tin oxide containing silicon oxide.

Although not illustrated in FIG. 21, alignment films may be provided ona side of the conductive film 772 in contact with the liquid crystallayer 776 and on a side of the conductive film 774 in contact with theliquid crystal layer 776. Although not illustrated in FIG. 21, anoptical member (an optical substrate) and the like such as a polarizingmember, a retardation member, or an anti-reflection member may beprovided as appropriate. For example, circular polarization may beemployed by using a polarizing substrate and a retardation substrate. Inaddition, a backlight, a sidelight, or the like may be used as a lightsource.

In the case where a liquid crystal element is used as the displayelement, a thermotropic liquid crystal, a low-molecular liquid crystal,a high-molecular liquid crystal, a polymer dispersed liquid crystal, aferroelectric liquid crystal, an anti-ferroelectric liquid crystal, orthe like can be used. Such a liquid crystal material exhibits acholesteric phase, a smectic phase, a cubic phase, a chiral nematicphase, an isotropic phase, or the like depending on conditions.

Alternatively, in the case of employing a horizontal electric fieldmode, a liquid crystal exhibiting a blue phase for which an alignmentfilm is unnecessary may be used. A blue phase is one of liquid crystalphases, which is generated just before a cholesteric phase changes intoan isotropic phase while temperature of cholesteric liquid crystal isincreased. Since the blue phase appears only in a narrow temperaturerange, a liquid crystal composition in which several weight percent ormore of a chiral material is mixed is used for the liquid crystal layerin order to improve the temperature range. The liquid crystalcomposition containing a liquid crystal showing a blue phase and achiral material has a short response time and optical isotropy, whicheliminates the need for an alignment process and reduces viewing angledependence. An alignment film does not need to be provided and rubbingtreatment is thus not necessary; accordingly, electrostatic dischargedamage caused by the rubbing treatment can be prevented and defects anddamage of the liquid crystal display device in the manufacturing processcan be reduced.

In the case where a liquid crystal element is used as the displayelement, a twisted nematic (TN) mode, an in-plane-switching (IPS) mode,a fringe field switching (FFS) mode, an axially symmetric alignedmicro-cell (ASM) mode, an optical compensated birefringence (OCB) mode,a ferroelectric liquid crystal (FLC) mode, an antiferroelectric liquidcrystal (AFLC) mode, or the like can be used.

Furthermore, a normally black liquid crystal display device such as atransmissive liquid crystal display device utilizing a verticalalignment (VA) mode may also be used. There are some examples of thevertical alignment mode; for example, a multi-domain vertical alignment(MVA) mode, a patterned vertical alignment (PVA) mode, an ASV mode, orthe like can be employed.

The display device 700 may include the protective film 799. FIGS. 22 and23 each illustrate an example in which the display device 700 includesthe protective film 799. In the example illustrated in FIG. 23, an endportion of the sealant has a recess. A method for forming the protectivefilm 799 is described here. First, the first substrate 701 provided withthe transistors and the like and the second substrate 705 provided withthe coloring film 736 and the like are attached to each other with thesealant 712. Next, the protective film 799 is formed by an ALD method.Note that the protective film 799 can be prevented from being formed ina connection portion for the anisotropic conductive film 780 or the likeby masking.

By an ALD method, a dense film can be formed extremely uniformly on asurface on which the film is formed. By using an ALD method, forexample, aluminum oxide, hafnium oxide, zirconium oxide, titanium oxide,zinc oxide, indium oxide, tin oxide, indium tin oxide (ITO), tantalumoxide, silicon oxide, manganese oxide, nickel oxide, erbium oxide,cobalt oxide, tellurium oxide, barium titanate, titanium nitride,tantalum nitride, aluminum nitride, tungsten nitride, cobalt nitride,manganese nitride, hafnium nitride, and the like can be deposited as theprotective film. Furthermore, the protective film is not limited to aninsulating film, and a conductive film may also be deposited. Forexample, ruthenium, platinum, nickel, cobalt, manganese, copper, and thelike can be deposited.

When the protective film 799 is formed on the side surface portion ofthe display panel by an ALD method, entry of external components such asmoisture can be inhibited. As a result, a change in transistorcharacteristics can be inhibited and the operation of the peripheralcircuit can be stable. Moreover, the frame size can be reduced, thepixel region can be enlarged, and the resolution of the display devicecan be increased.

With the protective film 799, even if a distance between an end portionof the peripheral circuit and the end portion of the substrate isdecreased, the stable transistor characteristics are obtained, that is,the peripheral circuit operates stably because of a high barrierproperty of the protective film 799; thus, the frame of the displaypanel can be narrowed. For example, the distance between the peripheralcircuit and the end portion of the substrate (a cut portion when thepanel is processed) can be 300 μm or shorter, preferably 200 μm orshorter. Alternatively, the end portion of the display panel may have astructure with unevenness as illustrated in FIG. 23.

[Display Device Using Light-Emitting Element as Display Element]

The display device 700 illustrated in FIG. 24 includes the capacitor 790b. The capacitor 790 b has a structure in which a dielectric is providedbetween a pair of electrodes. Specifically, a conductive film which isformed through the same process as a conductive film functioning as thegate electrode of the transistor 750 is used as one electrode of thecapacitor 790 b, and the conductive film functioning as the sourceelectrode or the drain electrode of the transistor 750 is used as theother electrode of the capacitor 790 b. Furthermore, an insulating filmfunctioning as a gate insulating film of the transistor 750 is used asthe dielectric between the pair of electrodes.

Furthermore, in FIG. 24, a planarization insulating film 770 is providedover the insulating film 768.

The planarization insulating film 770 can be formed using aheat-resistant organic material, such as a polyimide resin, an acrylicresin, a polyimide amide resin, a benzocyclobutene resin, a polyamideresin, and an epoxy resin. Note that the planarization insulating film770 may be formed by stacking a plurality of insulating films formedusing these materials. Alternatively, a structure without theplanarization insulating film 770 as illustrated in FIG. 21 may beemployed.

The display device 700 illustrated in FIG. 24 includes a light-emittingelement 782. The light-emitting element 782 includes a conductive film784, an EL layer 786, and a conductive film 788. The display device 700illustrated in FIG. 24 is capable of displaying an image by lightemission from the EL layer 786 included in the light-emitting element782.

The conductive film 784 is connected to the conductive film functioningas the source electrode or the drain electrode included in thetransistor 750. The conductive film 784 is formed over the planarizationinsulating film 770 to function as a pixel electrode, i.e., oneelectrode of the display element. A conductive film which transmitsvisible light or a conductive film which reflects visible light can beused for the conductive film 784. For example, a material including onekind selected from indium (In), zinc (Zn), and tin (Sn) is preferablyused for the conductive film that transmits visible light. For example,a material including aluminum or silver is preferably used for theconductive film that reflects visible light.

In the display device 700 illustrated in FIG. 24, an insulating film 730is provided over the planarization insulating film 770 and theconductive film 784. The insulating film 730 covers part of theconductive film 784. Note that the light-emitting element 782 has a topemission structure. Therefore, the conductive film 788 has alight-transmitting property and transmits light emitted from the ELlayer 786. Although the top-emission structure is described as anexample in this embodiment, one embodiment of the present invention isnot limited thereto. A bottom-emission structure in which light isemitted to the conductive film 784 side, or a dual-emission structure inwhich light is emitted to both the conductive film 784 side and theconductive film 788 side may be employed.

The coloring film 736 is provided to overlap with the light-emittingelement 782, and the light-blocking film 738 is provided to overlap withthe insulating film 730 and to be included in the lead wiring portion711 and in the source driver circuit portion 704. The coloring film 736and the light-blocking film 738 are covered with the insulating film734. A space between the light-emitting element 782 and the insulatingfilm 734 is filled with a sealing film 732. Although the coloring film736 is provided in the example of the display device 700 illustrated inFIG. 24, one embodiment of the present invention is not limited thereto.In the case where the EL layer 786 is formed by a separate coloringmethod, the coloring film 736 is not necessarily provided.

The display device 700 may include the protective film 799 asillustrated in FIG. 25. When the protective film 799 is formed in a sidesurface portion of the display panel by an ALD method, entry of externalcomponents such as moisture can be inhibited. This is preferableparticularly in the case where an organic EL layer is used as the ELlayer 786 because the inhibition of the entry of moisture can suppressthe deterioration of the EL layer and can increase the lifetime of thelight-emitting element.

The protective film 799 may be formed, for example, after the firstsubstrate 701 provided with the transistors, the light-emitting element,and the like and the second substrate 705 are attached to each other.

This embodiment can be implemented in appropriate combination with anyof the other embodiments.

Embodiment 3

In this embodiment, an example of a method for charging a power storagedevice by wireless power feeding will be described. For wireless powerfeeding, an electric field, a magnetic field, an electromagnetic wave,or the like can be used. An antenna, a coil, or the like can be used forreceiving an electric field, a magnetic field, an electromagnetic wave,or the like.

An electronic device of one embodiment of the present inventionpreferably includes an antenna, a coil, or the like for receiving anelectric field, a magnetic field, an electromagnetic wave, or the like.The electronic device of one embodiment of the present inventionpreferably includes a capacitor for charging.

When a coupling coil and a coupling capacitor are used, the powerstorage device can be charged without contact. An antenna can be usedinstead of a coupling coil. Here, a secondary battery is used as thepower storage device, for example. By an electromagnetic inductionmethod in which a primary coil of a charger and a secondary coil of theelectronic device are magnetically coupled and a voltage is generated atthe secondary coil with an alternating magnetic field generated from theprimary coil, electric power is transmitted to the secondary coil sidewithout contact. Through this mechanism, the secondary battery ischarged. It is preferable that the coil be provided in contact with acurved surface of a structure body; therefore, it is preferable that thecoil of the electronic device be provided over a flexible film. Here,the coil provided in the electronic device may be used as an antenna.

The secondary battery in an arm-worn electronic device including adisplay module may be provided with an antenna for purposes other thancontactless charging of the secondary battery. A memory may be furtherprovided, and an antenna that enables electronic data transmission andreception or an antenna that enables display of position or time with aGPS function by obtaining positional information or GPS time may beprovided.

Since the electronic device is to be in contact with part of a humanbody, it is preferable for safety that input and output terminals forcharging or discharging the secondary battery not be exposed. In thecase where the input and output terminals are exposed, the input andoutput terminals might short-circuit by water such as rain, or the inputand output terminals might be in contact with a human body and cause anelectric shock. The use of an antenna enables a structure in which theinput and output terminals are not exposed on a surface of theelectronic device.

Note that this embodiment is the same as Embodiment 1 except that anantenna, a coil, and a converter for wireless power feeding areprovided; therefore, the other components are not described in detailhere.

As in Embodiment 1, a power storage device, here, a secondary battery isfixed to a board, and a display module is attached to the secondarybattery. The secondary battery preferably has a bent shape. Furthermore,the secondary battery preferably has flexibility. A converter forwireless power feeding and an antenna which are electrically connectedto the secondary battery are provided. The converter for wireless powerfeeding is fixed so as to overlap with part of a display portion.

The converter for wireless power feeding and the antenna weigh less thanor equal to 10 g, and the total weight does not significantly differfrom that in Embodiment 1.

FIG. 12 is a schematic diagram of an electronic device 400 including anantenna (not illustrated) and a charger 401. When the electronic device400 is disposed over the charger 401, electric power can be suppliedfrom an antenna of the charger 401 to the electronic device 400 tocharge a secondary battery of the electronic device 400.

Information such as the remaining amount or time to full charge can bedisplayed on a display portion of the electronic device 400.

This embodiment can be implemented in appropriate combination with anyof the other embodiments.

Embodiment 4

In this embodiment, examples of a method for manufacturing the thinstorage battery described in Embodiment 1 and a structure of a coin-typestorage battery will be described.

[Method for Manufacturing Thin Secondary Battery]

A method for manufacturing the thin secondary battery whose exteriorbody includes a film, which is described in Embodiment 1, will bedescribed. FIG. 10 is an external view of the thin secondary battery.FIG. 11A illustrates a cross section taken along the dashed-dotted lineA1-A2 in FIG. 10, and FIG. 11B illustrates a cross section taken alongthe dashed-dotted line B1-B2 in FIG. 10.

A method for manufacturing the thin secondary battery will be described.

The separator 207 is preferably formed to have a bag-like shape tosurround one of the positive electrode 203 and the negative electrode206. For example, as illustrated in FIG. 13A, the separator 207 isfolded in two so that the positive electrode 203 is sandwiched, andsealed with a sealing member 514 in a region outside the regionoverlapping with the positive electrode 203; thus, the positiveelectrode 203 can be reliably supported inside the separator 207. Then,as illustrated in FIG. 13B, the positive electrodes 203 surrounded bythe separators 207 and the negative electrodes 206 are alternatelystacked and provided in the exterior body 209, whereby the thinsecondary battery can be formed.

FIG. 14B illustrates an example where a current collector is welded to alead electrode, specifically, an example where the positive electrodecurrent collectors 201 are welded to the positive electrode leadelectrode 510. The positive electrode current collectors 201 are weldedto the positive electrode lead electrode 510 in a welding region 512 byultrasonic welding or the like. The positive electrode current collector201 includes a bent portion 513 as illustrated in FIG. 14B, and it istherefore possible to relieve stress due to external force applied afterfabrication of the thin secondary battery. Thus, the thin secondarybattery can have high reliability.

In the thin secondary battery illustrated in FIGS. 13A and 13B and FIGS.14A and 14B, the positive electrode lead electrode 510 and the positiveelectrode current collectors 201 included in the positive electrodes 203are welded to each other by ultrasonic welding, and the negativeelectrode lead electrode 511 and the negative electrode currentcollectors 204 included in the negative electrodes 206 are welded toeach other by ultrasonic welding. The positive electrode currentcollector 201 and the negative electrode current collector 204 candouble as terminals for electrical contact with the outside. In thatcase, the positive electrode current collector 201 and the negativeelectrode current collector 204 may be arranged so that part of thepositive electrode current collector 201 and part of the negativeelectrode current collector 204 are exposed to the outside of theexterior body 209 without using lead electrodes.

Although the positive electrode lead electrode 510 and the negativeelectrode lead electrode 511 are provided on the same side in FIG. 10,the positive electrode lead electrode 510 and the negative electrodelead electrode 511 may be provided on different sides as illustrated inFIG. 15. The lead electrodes of a storage battery of one embodiment ofthe present invention can be freely positioned as described above;therefore, the degree of freedom in design is high. Accordingly, aproduct including a storage battery of one embodiment of the presentinvention can have a high degree of freedom in design. Furthermore, theyield of products each including a storage battery of one embodiment ofthe present invention can be increased.

As the exterior body 209 in the thin storage battery, for example, afilm having a three-layer structure in which a highly flexible metalthin film of aluminum, stainless steel, copper, nickel, or the like isprovided over a film formed of a material such as polyethylene,polypropylene, polycarbonate, ionomer, or polyamide, and an insulatingsynthetic resin film of a polyamide-based resin, a polyester-basedresin, or the like is provided as the outer surface of the exterior bodyover the metal thin film can be used.

The example in FIGS. 11A and 11B includes five sets of combinations ofpositive electrode and negative electrode active material layers (thepositive electrode and negative electrode active material layers of eachset face each other with a separator provided therebetween). It isneedless to say that the number of sets of combinations of activematerial layers is not limited to five, and may be more than five orless than five. In the case of using a large number of active materiallayers, the storage battery can have high capacity. In contrast, in thecase of using a small number of active material layers, the storagebattery can have a small thickness and high flexibility.

In the above structure, the exterior body 209 of the secondary batterycan change its shape with a radius of curvature greater than or equal to30 mm, preferably greater than or equal to 10 mm. One or two films areused as the exterior body of the secondary battery. In the case wherethe secondary battery has a layered structure, the secondary battery hasa cross section sandwiched between two curved surfaces of the films whenit is bent.

Description is given of the radius of curvature of a surface withreference to FIGS. 16A to 16C. In FIG. 16A, on a plane 1701 along whicha curved surface 1700 is cut, part of a curve 1702 of the curved surface1700 is approximate to an arc of a circle, and the radius of the circleis referred to as a radius 1703 of curvature and the center of thecircle is referred to as a center 1704 of curvature. FIG. 16B is a topview of the curved surface 1700. FIG. 16C is a cross-sectional view ofthe curved surface 1700 taken along the plane 1701. When a curvedsurface is cut by a plane, the radius of curvature of a curve in a crosssection differs depending on the angle between the curved surface andthe plane or on the cut position, and the smallest radius of curvatureis defined as the radius of curvature of a surface in this specificationand the like.

In the case of bending a secondary battery in which a component 1805including electrodes and an electrolytic solution is sandwiched betweentwo films as exterior bodies, a radius 1802 of curvature of a film 1801on the side closer to a center 1800 of curvature of the secondarybattery is smaller than a radius 1804 of curvature of a film 1803 on theside farther from the center 1800 of curvature (FIG. 17A). When thesecondary battery is curved and has an arc-shaped cross section,compressive stress is applied to a surface of the film on the sidecloser to the center 1800 of curvature and tensile stress is applied toa surface of the film on the side farther from the center 1800 ofcurvature (FIG. 17B). However, by forming a pattern includingprojections or depressions on surfaces of the exterior bodies, theinfluence of a strain can be reduced to be acceptable even whencompressive stress and tensile stress are applied. For this reason, thesecondary battery can change its shape such that the exterior body onthe side closer to the center of curvature has a curvature radiusgreater than or equal to 30 mm, preferably greater than or equal to 10mm.

Note that the cross-sectional shape of the secondary battery is notlimited to a simple arc shape, and the cross section can be partlyarc-shaped; for example, a shape illustrated in FIG. 17C, a wavy shapeillustrated in FIG. 17D, or an S shape can be used. When the curvedsurface of the secondary battery has a shape with a plurality of centersof curvature, the secondary battery can change its shape such that acurved surface with the smallest radius of curvature among radii ofcurvature with respect to the plurality of centers of curvature, whichis a surface of the exterior body on the side closer to the center ofcurvature, has a curvature radius greater than or equal to 30 mm,preferably greater than or equal to 10 mm.

Next, aging after fabrication of the secondary battery will bedescribed. Aging is preferably performed after fabrication of thesecondary battery. The aging can be performed under the followingconditions, for example. Charge is performed at a rate of 0.001 C ormore and 0.2 C or less at a temperature higher than or equal to roomtemperature and lower than or equal to 40° C., for example. In the casewhere an electrolytic solution is decomposed and a gas is generated andaccumulated in the cell, the electrolytic solution cannot be in contactwith a surface of the electrode in some regions. That is to say, aneffectual reaction area of the electrode is reduced and effectualcurrent density is increased.

When the current density is too high, a voltage drop occurs depending onthe resistance of the electrode, and deposition of lithium on thesurface of the active material proceeds in parallel with theintercalation of lithium into the active material. The lithiumdeposition might reduce capacity. For example, if a coating film or thelike grows on the surface after lithium deposition, lithium deposited onthe surface cannot be dissolved. This lithium cannot contribute tocapacity. In addition, when deposited lithium is physically collapsedand conduction with the electrode is lost, the lithium also cannotcontribute to capacity. Therefore, the gas is preferably released beforethe potential of the electrode reaches the potential of lithium becauseof a voltage drop.

After the release of the gas, the charging state may be maintained at atemperature higher than room temperature, preferably higher than orequal to 30° C. and lower than or equal to 60° C., more preferablyhigher than or equal to 35° C. and lower than or equal to 60° C. for,for example, 1 hour or more and 100 hours or less. In the initialcharge, an electrolytic solution decomposed on the surface forms acoating film. The formed coating film may thus be densified when thecharging state is held at a temperature higher than room temperatureafter the release of the gas, for example.

Here, in the case where the thin storage battery is bent, it ispreferably bent after the release of the gas. By bending the thinstorage battery after the release of the gas, for example, lithiumdeposition in a region to which stress is applied due to the bending orthe like can be prevented.

[Coin-Type Storage Battery]

Next, an example of a coin-type storage battery will be described as anexample of a power storage device with reference to FIGS. 18A and 18B.FIG. 18A is an external view of a coin-type (single-layer flat type)storage battery, and FIG. 18B is a cross-sectional view thereof.

In a coin-type storage battery 300, a positive electrode can 301doubling as a positive electrode terminal and a negative electrode can302 doubling as a negative electrode terminal are insulated from eachother and sealed by a gasket 303 made of polypropylene or the like. Anegative electrode 307 includes a negative electrode current collector308 and a negative electrode active material layer 309 provided incontact with the negative electrode current collector 308. The negativeelectrode active material layer 309 includes the negative electrodeactive material described in Embodiment 1. For the negative electrode307, the negative electrode described in Embodiment 2 is preferablyused.

A positive electrode 304 includes a positive electrode current collector305 and a positive electrode active material layer 306 provided incontact with the positive electrode current collector 305. Thedescription of the positive electrode active material layer 202 can bereferred to for the positive electrode active material layer 306. Thedescription of the separator 207 can be referred to for a separator 310.The description of the electrolytic solution 208 can be referred to foran electrolytic solution.

Note that only one surface of each of the positive electrode 304 and thenegative electrode 307 used for the coin-type storage battery 300 isprovided with an active material layer.

For the positive electrode can 301 and the negative electrode can 302, ametal having a corrosion-resistant property to an electrolytic solution,such as nickel, aluminum, or titanium, an alloy of such metals, and analloy of such a metal and another metal (e.g., stainless steel) can beused. Alternatively, the positive electrode can 301 and the negativeelectrode can 302 are preferably covered with nickel, aluminum, or thelike in order to prevent corrosion due to the electrolytic solution. Thepositive electrode can 301 and the negative electrode can 302 areelectrically connected to the positive electrode 304 and the negativeelectrode 307, respectively.

The negative electrode 307, the positive electrode 304, and theseparator 310 are immersed in the electrolytic solution. Then, asillustrated in FIG. 18B, the positive electrode 304, the separator 310,the negative electrode 307, and the negative electrode can 302 arestacked in this order with the positive electrode can 301 positioned atthe bottom, and the positive electrode can 301 and the negativeelectrode can 302 are subjected to pressure bonding with the gasket 303interposed therebetween. In such a manner, the coin-type storage battery300 can be manufactured.

This embodiment can be implemented in appropriate combination with anyof the other embodiments.

Embodiment 5

In this embodiment, a deposition method and a deposition apparatus whichcan be used for manufacture of a display device of one embodiment of thepresent invention will be described.

<<CVD and ALD>>

In a conventional deposition apparatus utilizing a CVD method, one or aplurality of source material gases (precursors) for reaction aresupplied to a chamber at the same time at the time of deposition. In adeposition apparatus utilizing an ALD method, precursors for reactionare sequentially introduced into a chamber, and then the sequence of thegas introduction is repeated. For example, two or more kinds ofprecursors are sequentially supplied to the chamber by switchingrespective switching valves (also referred to as high-speed valves). Forexample, a first precursor is introduced, an inert gas (e.g., argon ornitrogen) or the like is introduced after the introduction of the firstprecursor so that the plural kinds of precursors are not mixed, and thena second precursor is introduced. Alternatively, the first precursor maybe exhausted by vacuum evacuation instead of the introduction of theinert gas, and then the second precursor can be introduced.

FIGS. 27A to 27D illustrate a deposition process by an ALD method. Firstprecursors 601 are adsorbed onto a substrate surface (see FIG. 27A),whereby a first monolayer is formed (see FIG. 27B). At this time, metalatoms and the like included in the precursors can be bonded to hydroxylgroups that exist at the substrate surface. The metal atoms may bebonded to alkyl groups such as methyl groups or ethyl groups. The firstmonolayer reacts with second precursors 602 introduced after the firstprecursors 601 are evacuated (see FIG. 27C), whereby a second monolayeris stacked over the first monolayer. Thus, a thin film is formed (seeFIG. 27D). For example, in the case where an oxidizer is included in thesecond precursors, the oxidizer chemically reacts with metal atomsincluded in the first precursors or an alkyl group bonded to metalatoms, whereby an oxide film can be formed.

An ALD method is a deposition method based on a surface chemicalreaction, by which precursors are adsorbed onto a surface and adsorbingis stopped by a self-terminating mechanism, whereby a layer is formed.For example, precursors such as trimethylaluminum react with hydroxylgroups (OH groups) that exist at the surface. At this time, only asurface reaction due to heating occurs; therefore, the precursors comeinto contact with the surface and metal atoms or the like in theprecursors can be adsorbed onto the surface by thermal energy. Theprecursors have characteristics of, for example, having a high vaporpressure, being thermally stable and not decomposed before beingdeposited, and being chemically adsorbed onto a substrate at a highspeed. Since the precursors are introduced in a state of a gas, when thefirst precursors and the second precursors, which are alternatelyintroduced, have enough time to be diffused, a film can be formed withgood coverage even onto a region having unevenness with a high aspectratio.

In an ALD method, the sequence of the gas introduction is repeated aplurality of times until a desired thickness is obtained, whereby a thinfilm with excellent step coverage can be formed. The thickness of thethin film can be adjusted by the number of repetition times of thesequence of the gas introduction; therefore, an ALD method makes itpossible to accurately adjust a thickness. The deposition rate can beincreased and the impurity concentration in the film can be reduced byimproving the evacuation capability.

ALD methods include an ALD method using heating (thermal ALD method) andan ALD method using plasma (plasma ALD method). In the thermal ALDmethod, precursors react using thermal energy, and in the plasma ALDmethod, precursors react in a state of a radical.

By an ALD method, an extremely thin film can be formed with highaccuracy. In addition, the coverage of an uneven surface with the filmand the film density of the film are high.

Furthermore, plasma damage is not caused by the thermal ALD method.Therefore, generation of defects in a film can be inhibited.

<<Plasma ALD>>

Alternatively, when the plasma ALD method is employed, the film can beformed at a lower temperature than when the thermal ALD method isemployed. With the plasma ALD method, for example, the film can beformed without decreasing the deposition rate even at 100° C. or lower.Moreover, in the plasma ALD method, nitrogen radicals can be formed byplasma; thus, a nitride film as well as an oxide film can be formed.

In addition, oxidizability of an oxidizer can be enhanced by the plasmaALD method. Thus, precursors remaining in a plasma ALD film or organiccomponents released from precursors can be reduced. In addition, carbon,chlorine, hydrogen, and the like in the film can be reduced. Therefore,a film with low impurity concentration can be formed.

Furthermore, in the case where a light-emitting element (such as anorganic EL element) is used as a display element, when a processtemperature is high, the deterioration of the light-emitting element maybe accelerated. Here, with the plasma ALD method, the processtemperature can be lowered; thus, the deterioration of thelight-emitting element can be inhibited.

In the case of using the plasma ALD, inductively coupled plasma (ICP) isused to generate radical species. Accordingly, plasma can be generatedat a place apart from the substrate, so that plasma damage to thesubstrate or a film over the surface of which a plasma ALD film isformed can be inhibited.

As described above, with the plasma ALD method, the process temperaturecan be lowered and the coverage of the surface can be increased ascompared with other deposition methods, and a plasma ALD film can beformed on the side surface portion of the substrate after the displaypanel is fabricated. Thus, entry of water from the outside can beinhibited. Therefore, the reliability of driver operation of aperipheral circuit at a panel end portion is improved (the transistorcharacteristics are improved), so that a stable operation can beachieved even in the case of employing a narrow frame.

Next, an example of a deposition apparatus ALD will be described withreference to FIG. 28 as a deposition apparatus which can be used formanufacture of a display device of one embodiment of the presentinvention.

[Structural Example of Deposition Apparatus ALD]

FIG. 28 is a cross-sectional view of a deposition apparatus ALD whichcan be used for manufacture of a display module of one embodiment of thepresent invention. The deposition apparatus ALD described in thisembodiment includes a deposition chamber 180 and a control portion 182connected to the deposition chamber 180.

The control portion 182 includes a control unit (not illustrated) whichsupplies control signals and flow rate controllers 182 a, 182 b, and 182c to which the control signals are supplied. For example, high-speedvalves can be used as the flow rate controllers. Specifically, flowrates can be precisely controlled by using ALD valves or the like. Thecontrol portion 182 also includes a heating mechanism 182 h whichcontrols the temperatures of the flow rate controllers and pipes.

The flow rate controller 182 a is supplied with a control signal, afirst source material, and an inert gas and has a function of supplyingthe first source material or the inert gas in accordance with thecontrol signal.

The flow rate controller 182 b is supplied with a control signal, asecond source material, and an inert gas and has a function of supplyingthe second source material or the inert gas in accordance with thecontrol signal.

The flow rate controller 182 c is supplied with a control signal and hasa function of connecting to an evacuation unit 185 in accordance withthe control signal.

<<Source Material Supply Portion>>

A source material supply portion 181 a has a function of supplying thefirst source material and is connected to the flow rate controller 182a.

A source material supply portion 181 b has a function of supplying thesecond source material and is connected to the flow rate controller 182b.

A vaporizer, a heating unit, or the like can be used as each of thesource material supply portions. Thus, a gaseous source material can begenerated from a solid or liquid source material.

Note that the number of source material supply portions is not limitedto two and may be three or more.

<<Source Material>>

Any of a variety of substances can be used as the first source material.

For example, a volatile organometallic compound, a volatile metalalkoxide, or the like can be used as the first source material.

Any of a variety of substances which react with the first sourcematerial can be used as the second source material. For example, asubstance which contributes to an oxidation reaction, a substance whichcontributes to a reduction reaction, a substance which contributes to anaddition reaction, a substance which contributes to a decompositionreaction, a substance which contributes to a hydrolysis reaction, or thelike can be used as the second source material.

Furthermore, a radical or the like can be used. For example, plasmaobtained by supplying a source material to a plasma source or the likecan be used. Specifically, an oxygen radical, a nitrogen radical, or thelike can be used.

A high-frequency power source or a light source can be used as theplasma source. For example, an inductively coupled or capacitivelycoupled high-frequency power source can be used. Alternatively, anexcimer laser, an excimer lamp, a low-pressure mercury lamp, or asynchrotron radiation source can be used as the light source. The secondsource material is preferably a source material which reacts with thefirst source material at a temperature close to room temperature. Forexample, a source material which reacts at a temperature higher than orequal to room temperature and lower than or equal to 200° C., preferablyhigher than or equal to 50° C. and lower than or equal to 150° C., ispreferable.

<<Evacuation Unit 185>>

The evacuation unit 185 has an evacuating function and is connected tothe flow rate controller 182 c. Note that a trap for capturing thesource material to be evacuated may be provided between an outlet port184 and the flow rate controller 182 c. A dry pump, a turbo pump, and/orthe like can be used as the evacuation unit 185. The time required forevacuation can be shortened by using a turbo pump. The evacuated gas orthe like is removed by using a removal unit.

<<Control Portion 182>>

The control unit supplies the control signals for controlling the flowrate controllers, a control signal for controlling the heatingmechanism, or the like. For example, in a first step, the first sourcematerial is supplied to a surface of a process base. Then, in a secondstep, the second source material which reacts with the first sourcematerial is supplied. Accordingly, a reaction product of the firstsource material and the second source material can be deposited onto asurface of a process member 10.

Note that the amount of the reaction product to be deposited onto thesurface of the process member 10 can be controlled by a repetition ofthe first step and the second step.

Note that the amount of the first source material to be supplied to theprocess member 10 is limited by the maximum possible amount ofadsorption on the surface of the process member 10. For example,conditions are selected so that a monomolecular layer of the firstsource material is formed on the surface of the process member 10, andthe formed monomolecular layer of the first source material is reactedwith the second source material, whereby a significantly uniform layercontaining the reaction product of the first source material and thesecond source material can be formed.

Accordingly, a variety of materials can be deposited on a surface of theprocess member 10 even when the surface has a complicated structure. Forexample, a film having a thickness greater than or equal to 3 nm andless than or equal to 200 nm can be formed on the process member 10.

In the case where, for example, a small hole called a pinhole or thelike is formed in the surface of the process member 10, the pinhole canbe filled by depositing a material into the pinhole.

The remainder of the first source material or the second source materialis evacuated from the deposition chamber 180 with use of the evacuationunit 185. For example, the evacuation may be performed while an inertgas such as argon or nitrogen is introduced.

<<Deposition Chamber 180>>

The deposition chamber 180 includes an inlet port 183 from which thefirst source material, the second source material, and the inert gas aresupplied and the outlet port 184 from which the first source material,the second source material, and the inert gas are evacuated.

The deposition chamber 180 includes a support portion 186 which has afunction of supporting one or a plurality of process members 10, aheating mechanism 187 which has a function of heating the one orplurality of process members, and a door 188 which has a function ofopening or closing to load and unload the one or plurality of processmembers 10.

For example, a resistive heater, an infrared lamp, or the like can beused as the heating mechanism 187.

The heating mechanism 187 has a function of heating up, for example, to80° C. or higher, 100° C. or higher, or 150° C. or higher.

The heating mechanism 187 heats the one or plurality of process members10 to a temperature higher than or equal to room temperature and lowerthan or equal to 200° C., preferably higher than or equal to 50° C. andlower than or equal to 150° C.

The deposition chamber 180 also includes a pressure regulator and apressure detector.

<<Support Portion 186>>

The support portion 186 supports the one or plurality of process members10. Accordingly, an insulating film, for example, can be formed over theone or plurality of process members 10 in each treatment.

<Example of Film>

Films which can be formed using the deposition apparatus ALD describedin this embodiment will be described.

For example, a film containing an oxide, a nitride, a fluoride, asulfide, a ternary compound, a metal, or a polymer can be formed.

For example, a material containing aluminum oxide, hafnium oxide,aluminum silicate, hafnium silicate, lanthanum oxide, silicon oxide,strontium titanate, tantalum oxide, titanium oxide, zinc oxide, niobiumoxide, zirconium oxide, tin oxide, yttrium oxide, cerium oxide, scandiumoxide, erbium oxide, vanadium oxide, indium oxide, or the like can bedeposited.

For example, a material containing aluminum nitride, hafnium nitride,silicon nitride, tantalum nitride, titanium nitride, niobium nitride,molybdenum nitride, zirconium nitride, gallium nitride, or the like canbe deposited.

For example, a material containing copper, platinum, ruthenium,tungsten, iridium, palladium, iron, cobalt, nickel, or the like can bedeposited.

For example, a material containing zinc sulfide, strontium sulfide,calcium sulfide, lead sulfide, calcium fluoride, strontium fluoride,zinc fluoride, or the like can be deposited.

For example, a material that includes a nitride containing titanium andaluminum, an oxide containing titanium and aluminum, an oxide containingaluminum and zinc, a sulfide containing manganese and zinc, a sulfidecontaining cerium and strontium, an oxide containing erbium andaluminum, an oxide containing yttrium and zirconium, or the like can bedeposited.

<<Film Containing Aluminum Oxide>>

For example, a gas obtained by vaporizing a source material containingan aluminum precursor compound can be used as the first source material.Specifically, trimethylaluminum (TMA, or Al(CH₃)₃ (chemical formula)),tris(dimethylamide)aluminum, triisobutylaluminum, and aluminumtris(2,2,6,6-tetramethyl-3,5-heptanedionate), or the like can be used.

Water vapor (H₂O (chemical formula)) can be used as the second sourcematerial.

With the use of the deposition apparatus ALD, a film containing aluminumoxide can be formed from the first source material and the second sourcematerial.

<<Film Containing Hafnium Oxide>>

For example, a gas obtained by vaporizing a source material containing ahafnium precursor compound can be used as the first source material.Specifically, a source material containing hafnium amide such astetrakis(dimethylamide)hafnium (TDMAH, or Hf[N(CH₃)₂]₄ (chemicalformula)) or tetrakis(ethylmethylamide)hafnium can be used.

Ozone can be used as the second source material.

<<Film Containing Tungsten>>

For example, a WF₆ gas can be used as the first source material.

A B₂H₆ gas, a SiH₄ gas, or the like can be used as the second sourcematerial.

This embodiment can be implemented in appropriate combination with anyof the other embodiments.

Embodiment 6

In this embodiment, a structure of an oxide semiconductor film isdescribed.

An oxide semiconductor film is classified into a non-single-crystaloxide semiconductor film and a single crystal oxide semiconductor film.Alternatively, an oxide semiconductor is classified into, for example, acrystalline oxide semiconductor and an amorphous oxide semiconductor.

Examples of a non-single-crystal oxide semiconductor include a c-axisaligned crystalline oxide semiconductor (CAAC-OS), a polycrystallineoxide semiconductor, a microcrystalline oxide semiconductor, and anamorphous oxide semiconductor. In addition, examples of a crystallineoxide semiconductor include a single crystal oxide semiconductor, aCAAC-OS, a polycrystalline oxide semiconductor, and a microcrystallineoxide semiconductor.

First, a CAAC-OS film will be described.

The CAAC-OS film is one of oxide semiconductor films having a pluralityof c-axis aligned crystal parts.

In a combined analysis image (also referred to as a high-resolution TEMimage) of a bright-field image and a diffraction pattern of a CAAC-OSfilm, which is obtained using a transmission electron microscope (TEM),a plurality of crystal parts can be observed. However, in thehigh-resolution TEM image, a boundary between crystal parts, that is, agrain boundary is not clearly observed. Thus, in the CAAC-OS film, areduction in electron mobility due to the grain boundary is less likelyto occur.

According to the high-resolution cross-sectional TEM image of theCAAC-OS film observed in a direction substantially parallel to a samplesurface, metal atoms are arranged in a layered manner in the crystalparts. Each metal atom layer has a morphology reflecting unevenness of asurface where the CAAC-OS film is formed (hereinafter, a surface wherethe CAAC-OS film is formed is also referred to as a formation surface)or a top surface of the CAAC-OS film, and is arranged parallel to theformation surface or the top surface of the CAAC-OS film.

On the other hand, according to the high-resolution plan-view TEM imageof the CAAC-OS film observed in a direction substantially perpendicularto the sample surface, metal atoms are arranged in a triangular orhexagonal configuration in the crystal parts. However, there is noregularity of arrangement of metal atoms between different crystalparts.

A CAAC-OS film is subjected to structural analysis with an X-raydiffraction (XRD) apparatus. For example, when the CAAC-OS filmincluding an InGaZnO₄ crystal is analyzed by an out-of-plane method, apeak appears frequently when the diffraction angle (2θ) is around 31°.This peak is assigned to the (009) plane of the InGaZnO₄ crystal, whichindicates that crystals in the CAAC-OS film have c-axis alignment, andthat the c-axes are aligned in a direction substantially perpendicularto the formation surface or the top surface of the CAAC-OS film.

Note that when the CAAC-OS film with an InGaZnO₄ crystal is analyzed byan out-of-plane method, a peak may also be observed when 2θ is around36°, in addition to the peak at 2θ of around 31°. The peak at 2θ ofaround 36° indicates that a crystal having no c-axis alignment isincluded in part of the CAAC-OS film. It is preferable that in theCAAC-OS film, a peak appear when 2θ is around 31° and that a peak notappear when 2θ is around 36°.

The CAAC-OS film is an oxide semiconductor film having low impurityconcentration. The impurity is an element other than the main componentsof the oxide semiconductor film, such as hydrogen, carbon, silicon, or atransition metal element. In particular, an element that has higherbonding strength to oxygen than a metal element included in the oxidesemiconductor film, such as silicon, disturbs the atomic arrangement ofthe oxide semiconductor film by depriving the oxide semiconductor filmof oxygen and causes a decrease in crystallinity. Further, a heavy metalsuch as iron or nickel, argon, carbon dioxide, or the like has a largeatomic radius (molecular radius), and thus disturbs the atomicarrangement of the oxide semiconductor film and causes a decrease incrystallinity when it is contained in the oxide semiconductor film. Notethat the impurity contained in the oxide semiconductor film might serveas a carrier trap or a carrier generation source.

The CAAC-OS film is an oxide semiconductor film having a low density ofdefect states. In some cases, oxygen vacancies in the oxidesemiconductor film serve as carrier traps or serve as carrier generationsources when hydrogen is captured therein.

The state in which impurity concentration is low and density of defectstates is low (the number of oxygen vacancies is small) is referred toas a highly purified intrinsic or substantially highly purifiedintrinsic state. A highly purified intrinsic or substantially highlypurified intrinsic oxide semiconductor film has few carrier generationsources, and thus can have a low carrier density. Therefore, atransistor including the oxide semiconductor film rarely has negativethreshold voltage (is rarely normally on). The highly purified intrinsicor substantially highly purified intrinsic oxide semiconductor film hasfew carrier traps. Accordingly, the transistor including the oxidesemiconductor film has little variation in electrical characteristicsand high reliability. Electric charge trapped by the carrier traps inthe oxide semiconductor film takes a long time to be released and mightbehave like fixed electric charge. Thus, the transistor including theoxide semiconductor film having high impurity concentration and a highdensity of defect states has unstable electrical characteristics in somecases.

The characteristics of an oxide semiconductor having impurities ordefects might be changed by light, heat, or the like. Impuritiescontained in the oxide semiconductor might serve as carrier traps orcarrier generation sources, for example. Furthermore, oxygen vacanciesin the oxide semiconductor serve as carrier traps or serve as carriergeneration sources when hydrogen is captured therein.

The CAAC-OS having small amounts of impurities and oxygen vacancies isan oxide semiconductor with low carrier density. Specifically, an oxidesemiconductor with a carrier density of lower than 8×10¹¹/cm³,preferably lower than 1×10¹¹/cm³, further preferably lower than1×10¹⁰/cm³, and higher than or equal to 1×10⁻⁹/cm³ can be used. Such anoxide semiconductor is referred to as a highly purified intrinsic orsubstantially highly purified intrinsic oxide semiconductor. A CAAC-OShas a low impurity concentration and a low density of defect states.Thus, the CAAC-OS can be referred to as an oxide semiconductor havingstable characteristics.

With the use of the CAAC-OS film in a transistor, variation in theelectrical characteristics of the transistor due to irradiation withvisible light or ultraviolet light is small.

Next, a microcrystalline oxide semiconductor film will be described.

A microcrystalline oxide semiconductor film has a region in which acrystal part is observed and a region in which a crystal part is notclearly observed in a high-resolution TEM image. In most cases, the sizeof a crystal part included in the microcrystalline oxide semiconductorfilm is greater than or equal to 1 nm and less than or equal to 100 nm,or greater than or equal to 1 nm and less than or equal to 10 nm. Amicrocrystal with a size greater than or equal to 1 nm and less than orequal to 10 nm, or a size greater than or equal to 1 nm and less than orequal to 3 nm, is specifically referred to as nanocrystal (nc). An oxidesemiconductor film including nanocrystal is referred to as an nc-OS(nanocrystalline oxide semiconductor) film. In a high-resolution TEMimage of the nc-OS film, for example, a grain boundary is not clearlyobserved in some cases.

In the nc-OS film, a microscopic region (for example, a region with asize greater than or equal to 1 nm and less than or equal to 10 nm, inparticular, a region with a size greater than or equal to 1 nm and lessthan or equal to 3 nm) has a periodic atomic arrangement. There is noregularity of crystal orientation between different crystal parts in thenc-OS film. Thus, the orientation of the whole film is not observed.Accordingly, in some cases, the nc-OS film cannot be distinguished froman amorphous oxide semiconductor film depending on an analysis method.For example, when the nc-OS film is subjected to structural analysis byan out-of-plane method with an XRD apparatus using an X-ray having adiameter larger than the size of a crystal part, a peak indicating acrystal plane does not appear. Further, a halo pattern is shown in aselected-area electron diffraction pattern of the nc-OS film obtained byusing an electron beam having a probe diameter (e.g., 50 nm or larger)larger than the size of a crystal part. Meanwhile, spots are shown in ananobeam electron diffraction pattern of the nc-OS film obtained byusing an electron beam having a probe diameter close to or smaller thanthe size of a crystal part. Furthermore, in a nanobeam electrondiffraction pattern of the nc-OS film, regions with high luminance in acircular (ring) pattern are shown in some cases. Moreover, in a nanobeamelectron diffraction pattern of the nc-OS film, a plurality of spots areshown in a ring-like region in some cases.

The nc-OS film is an oxide semiconductor film that has high regularityas compared with an amorphous oxide semiconductor film. Therefore, thenc-OS film has a lower density of defect states than an amorphous oxidesemiconductor film. Note that there is no regularity of crystalorientation between different crystal parts in the nc-OS film.Therefore, the nc-OS film has a higher density of defect states than theCAAC-OS film.

Next, an amorphous oxide semiconductor film will be described.

The amorphous oxide semiconductor film has disordered atomic arrangementand no crystal part. For example, the amorphous oxide semiconductor filmdoes not have a specific state as in quartz.

In a high-resolution TEM image of the amorphous oxide semiconductorfilm, crystal parts cannot be found.

When the amorphous oxide semiconductor film is subjected to structuralanalysis by an out-of-plane method with an XRD apparatus, a peak whichshows a crystal plane does not appear. A halo pattern is observed whenthe amorphous oxide semiconductor film is subjected to electrondiffraction. Furthermore, a spot is not observed and a halo patternappears when the amorphous oxide semiconductor film is subjected tonanobeam electron diffraction.

Note that an oxide semiconductor film may have a structure havingphysical properties intermediate between the nc-OS film and theamorphous oxide semiconductor film. The oxide semiconductor film havingsuch a structure is specifically referred to as an amorphous-like oxidesemiconductor (a-like OS) film.

In a high-resolution TEM image of the a-like OS film, a void may beobserved. Furthermore, in the high-resolution TEM image, there are aregion where a crystal part is clearly observed and a region where acrystal part is not observed. In some cases, growth of the crystal partoccurs due to the crystallization of the a-like OS film, which isinduced by a slight amount of electron beam employed in the TEMobservation. In contrast, in the nc-OS film that has good quality,crystallization hardly occurs by a slight amount of electron beam usedfor TEM observation.

Note that the crystal part size in the a-like OS film and the nc-OS filmcan be measured using high-resolution TEM images. For example, anInGaZnO₄ crystal has a layered structure in which two Ga—Zn—O layers areincluded between In—O layers. A unit cell of the InGaZnO₄ crystal has astructure in which nine layers including three In—O layers and sixGa—Zn—O layers are stacked in the c-axis direction. Accordingly, thedistance between the adjacent layers is equivalent to the latticespacing on the (009) plane (also referred to as d value). The value iscalculated to be 0.29 nm from crystal structural analysis. Thus,focusing on lattice fringes in the high-resolution TEM image, each oflattice fringes in which the lattice spacing therebetween is greaterthan or equal to 0.28 nm and less than or equal to 0.30 nm correspondsto the a-b plane of the InGaZnO₄ crystal.

Furthermore, the density of an oxide semiconductor film varies dependingon the structure in some cases. For example, when the composition of anoxide semiconductor film is determined, the structure of the oxidesemiconductor film can be expected by comparing the density of the oxidesemiconductor film with the density of a single crystal oxidesemiconductor having the same composition as the oxide semiconductorfilm. For example, the density of the a-like OS film is higher than orequal to 78.6% and lower than 92.3% of the density of the single crystaloxide semiconductor having the same composition. For example, thedensity of each of the nc-OS film and the CAAC-OS film is higher than orequal to 92.3% and lower than 100% of the density of the single crystaloxide semiconductor having the same composition. Note that it isdifficult to deposit an oxide semiconductor film having a density oflower than 78% of the density of the single crystal oxide semiconductor.

Specific examples of the above description are given. For example, inthe case of an oxide semiconductor film having an atomic ratio ofIn:Ga:Zn=1:1:1, the density of single crystal InGaZnO₄ with arhombohedral crystal structure is 6.357 g/cm³. Accordingly, in the caseof the oxide semiconductor film having an atomic ratio ofIn:Ga:Zn=1:1:1, the density of the a-like OS film is higher than orequal to 5.0 g/cm³ and lower than 5.9 g/cm³. For example, in the case ofthe oxide semiconductor film having an atomic ratio of In:Ga:Zn=1:1:1,the density of each of the nc-OS film and the CAAC-OS film is higherthan or equal to 5.9 g/cm³ and lower than 6.3 g/cm³.

Note that there is a possibility that an oxide semiconductor having acertain composition cannot exist in a single crystal structure. In thatcase, single crystal oxide semiconductors with different compositionsare combined at an adequate ratio, which makes it possible to calculatedensity equivalent to that of a single crystal oxide semiconductor withthe desired composition. The density of a single crystal oxidesemiconductor having the desired composition can be calculated using aweighted average according to the combination ratio of the singlecrystal oxide semiconductors with different compositions. Note that itis preferable to use as few kinds of single crystal oxide semiconductorsas possible to calculate the density.

Note that an oxide semiconductor film may be a stacked film includingtwo or more films of an amorphous oxide semiconductor film, an a-like OSfilm, a microcrystalline oxide semiconductor film, and a CAAC-OS film,for example.

This embodiment can be implemented in appropriate combination with anyof the other embodiments.

This application is based on Japanese Patent Application serial no.2014-242053 filed with Japan Patent Office on Nov. 28, 2014, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. An electronic device comprising: a first board; a second board facing the first board; a display portion between the first board and the second board, the display portion having flexibility; and a power storage device between the first board and the second board, the power storage device having flexibility, wherein the display portion comprises a first surface facing the power storage device, wherein the first surface comprises a first region which is not in contact with the power storage device, and wherein the first region overlaps with a display region of the display portion.
 2. The electronic device according to claim 1, further comprising a space between the display portion and the power storage device.
 3. The electronic device according to claim 1, further comprising a shock-absorbing buffer member between the display portion and the power storage device.
 4. The electronic device according to claim 1, wherein the display portion comprises a first end portion and a second end portion, wherein the power storage device comprises a third end portion and a fourth end portion, wherein the first end portion and the third end portion are fixed to each other, and wherein a distance between the second end portion and the fourth end portion changes when a shape of the electronic device changes.
 5. The electronic device according to claim 1, further comprising a circuit board, wherein the display portion comprises a first end portion and a second end portion, wherein the power storage device comprises a third end portion and a fourth end portion, wherein the first end portion and the third end portion are fixed to the circuit board, and wherein a distance between the second end portion and the fourth end portion changes when a shape of the electronic device changes.
 6. The electronic device according to claim 1, wherein the electronic device is configured to be worn such that the second board is in contact with a user's arm.
 7. An electronic device comprising: a first board; a second board facing the first board; a display portion between the first board and the second board, the display portion having flexibility; a power storage device between the first board and the second board, the power storage device having flexibility; and an adhesive layer, wherein the display portion is provided on the first board with the adhesive layer provided therebetween, wherein the power storage device is in contact with the second board, and wherein a region of the power storage device is apart from the first board.
 8. The electronic device according to claim 7, further comprising a space between the display portion and the power storage device.
 9. The electronic device according to claim 7, further comprising a shock-absorbing buffer member between the display portion and the power storage device.
 10. The electronic device according to claim 7, wherein the display portion comprises a first end portion and a second end portion, wherein the power storage device comprises a third end portion and a fourth end portion, wherein the first end portion and the third end portion are fixed to each other, and wherein a distance between the second end portion and the fourth end portion changes when a shape of the electronic device changes.
 11. The electronic device according to claim 7, further comprising a circuit board, wherein the display portion comprises a first end portion and a second end portion, wherein the power storage device comprises a third end portion and a fourth end portion, wherein the first end portion and the third end portion are fixed to the circuit board, and wherein a distance between the second end portion and the fourth end portion changes when a shape of the electronic device changes.
 12. The electronic device according to claim 7, wherein the electronic device is configured to be worn such that the second board is in contact with a user's arm.
 13. An electronic device comprising: a first housing having flexibility; a display portion inside the first housing, the display portion having flexibility; a second housing facing the first housing, the second housing having flexibility; and a power storage device inside the second housing, the power storage device having flexibility, wherein the first housing comprises a first surface having a light-transmitting property, wherein a first surface of the display portion is in contact with the first surface of the first housing, and wherein the second housing is in contact with the first housing.
 14. The electronic device according to claim 13, wherein the second housing comprises a screw.
 15. The electronic device according to claim 13, wherein the electronic device is configured to be worn such that the second housing is in contact with a user's arm.
 16. The electronic device according to claim 13, wherein the display portion comprises a display element on a first surface side of the display portion, and wherein the display element and the first surface of the first housing overlap each other. 